document_title: List of largest stars

question_text: which is the largest sun in the universe

text: List of largest stars

text: Caveats

text: Complex issues exist in determining the true radii of the largest stars, which in many cases do display significant errors. The following lists are generally based on various considerations or assumptions that include:

text:
Largest stars are usually expressed in units of the solar radius (R☉), where 1.00 R☉ equals 695,700 kilometres.
Stellar radii or diameters are usually only approximated using Stefan–Boltzmann law for the deduced stellar luminosity and effective surface temperature;
Stellar distances, and their errors, for most, remain uncertain or poorly determined;
Many supergiant stars have extended atmospheres and many are embedded within opaque dust shells, making their true effective temperatures highly uncertain;
Many extended supergiant atmospheres also significantly change in size over time, regularly or irregularly pulsating over several months or years as variable stars.  This makes adopted luminosities poorly known and may significantly change the quoted radii;
Other direct methods for determining stellar radii, rely on lunar occultations or from eclipses in binary systems.  This is only possible for a very small number of stars;
Based on various theoretical evolutionary models, few stars will exceed 1,500–2,000 times the Sun (roughly 3,715 K and Mbol = −9). Such limits maybe also depend on the stellar metallicity.[1]

text: Extragalactic large stars

text: In this list are some examples of more distant extragalactic stars, which may have slightly different properties and natures than the currently largest known stars in the Milky Way:

text:
Some red supergiants in the Magellanic Clouds are suspected to have slightly different limiting temperatures and luminosities. Such stars may exceed accepted limits by undergoing large eruptions or change their spectral types over just a few months. Humphreys et al., for example, calculates the maximum size for a Magellanic cloud star as ~2,600 R☉.[citation needed]
A survey of the Magellanic Clouds has catalogued many red supergiants, where more than 50 of them exceed 700 R☉ (490,000,000 km; 3.3 AU; 300,000,000 mi). Largest of these is about 1,200–1,300 R☉.[2]

text: List

text:
List of the largest stars

Star name

Solar radii(Sun = 1)

Method[a]

Notes

Orbit of Saturn
1,940–2,169

Reported for reference

UY Scuti
1,708 ± 192[3]
AD
The quoted size was based on an angular diameter and distance of 2.9 kpc. Gaia Data Release 2 suggests a much closer distance and consequently smaller radius.

WOH G64
1,540[4]–1,730[5]
L/Teff
This would be the largest star in the LMC, but is unusual in position and motion and might still be a foreground halo giant.

RW Cephei
 1,535[6][7]
L/Teff
RW Cep is variable both in brightness (by at least a factor of 3) and spectral type (observed from G8 to M), thus probably also in diameter.  Because the spectral type and temperature at maximum luminosity are not known, the quoted size is just an estimate.

Westerlund 1-26
 1,530–1,580[8] (–2,550) [9]
L/Teff
Very uncertain parameters for an unusual star with strong radio emission.  The spectrum is variable but apparently the luminosity is not.

HD 143183
1,480[10]–1,830[11]
L/Teff

VY Canis Majoris
1,420 ± 120[12]
AD
The size of VY CMa was revised in 2012 through newly improved measurements[13] which result this value being the highest among well-characterized stars.[14] Other stars could be larger but they could have less accurate radius estimates.

KY Cygni
 1,420–2,850 [1]
L/Teff
The upper estimate is due to an unusual K-band measurement and thought to be an artifact of a reddening correction error, and is thought to be against stellar evolutionary theory. The lower estimate is consistent with other stars in the same survey and with theoretical models.

AH Scorpii
1,411 ± 124[3]
AD
AH Sco is variable by nearly 3 magnitudes in the visual range, and an estimated 20% in total luminosity.  The variation in diameter is not clear because the temperature also varies.

RSGC1-F02
1,398[15]
L/Teff

IRAS 04509-6922
1,360[16]
L/Teff

RSGC1-F01
1,335[15]
L/Teff

HR 5171 A
1,315 ± 260,[17] 1,575 ± 400[18]
AD
HR 5171 A is a highly distorted star in a close binary system, losing mass to the secondary, and is also variable in temperature, thus probably also in diameter. Traditionally, it is considered as the largest known yellow hypergiant, although the latest research suggests it is a red supergiant with a radius of 1,490 ± 540 R☉.[19]

SMC 18136
1,310[2]

Largest star in the Small Magellanic Cloud

IRAS 05280-6910
1,260[16] - 1,738[20]
L/Teff

Mu Cephei (Herschel's "Garnet Star")
1,260[21]

Prototype of the obsolete class of the Mu Cephei variables and also the reddest star in the night sky in terms of the B-V color index.[22] Other recent estimates range from 650 R☉[23] to 1,420 R☉[1]

LMC 136042
1,240[2]

BI Cygni
1,240[1]
L/Teff

Westerlund 1-237
1,233[9]
L/Teff

SMC 5092
1,220[2]

S Persei
1,212 ± 124[24]
AD &  L/Teff
A red hypergiant localed in the Perseus Double Cluster. A large radius of 1,230 R☉ is due to an unusual K-band measurement and thought to be an artifact of a reddening correction error. A small radius of 780 R☉ is consistent with other stars in the same survey and with theoretical models.[1]

LMC 175464
1,200[2]

LMC 135720
1,200[2]

IRC-10414
1,200[25]

IRC -10414 is a rare red supergiant companion to WR 114 that has a bow shock.

PZ Cassiopeiae
1,190–1,940[1]
L/Teff
The upper estimate is due to an unusual K-band measurement and thought to be an artefact of a reddening correction error. The lower estimate is consistent with other stars in the same survey and with theoretical models, and the intermediate ones have been obtained refining the distance to this star, and thus its parameters.[26]

SMC 69886
1,190[2]

NML Cygni
1,183[27]
L/Teff

RSGC1-F05
1,177[15]
L/Teff

EV Carinae
1,168[28]-2,880[29]
L/Teff

RSGC1-F03
1,168[15]
L/Teff

LMC 119219
1,150[2]

RSGC1-F08
1,146[15]
L/Teff

BC Cygni
1,140[1]-1,230[21]
L/Teff
BC Cyg is calculated to vary in size from 856 R☉ to 1,553 R☉.[30]

MY Cephei
1,134[31]
L/Teff
One of the coolest known red supergiants.

SMC 10889
1,130[2]

VX Sagittarii
1,120 - 1,550[32]
L/Teff
VX Sgr is a pulsating variable calculated to vary in size from 1,350 R☉ to 1,940 R☉.[33]

LMC 141430
1,110[2]

IRAS 04516-6902
1,100[16]
L/Teff

LMC 175746
1,100[2]

RSGC1-F13
1,098[15]
L/Teff

RT Carinae
1,090[1]
L/Teff

RSGC1-F04
1,082[15]
L/Teff

LMC 174714
1,080[2]

LMC 68125
1,080[2]

SMC 49478
1,080[2]

SMC 20133
1,080[2]

V396 Centauri
1,070[1]
L/Teff

SMC 8930
1,070[2]

Orbit of Jupiter
1,064–1,173

 Reported for reference

HV 11423
1,060–1,220[34]
L/Teff
HV 11423 is variable in spectral type (observed from K0 to M5), thus probably also in diameter. In October 1978, it was a star of M0I type.

CK Carinae
1,060[1]
L/Teff

SMC 25879
1,060[2]

VV Cephei A
1,050[35] -  1,900[1]

VV Cep A is a highly distorted star in a close binary system, losing mass to the secondary for at least part of its orbit.  Data from the most recent eclipse has cast additional doubt on the accepted model of the system. It is among the largest stars visible to the naked eye.

LMC 142202
1,050[2]

LMC 146126
1,050[2]

LMC 67982
1,040[2]

U Lacertae
1,022[36][37]
L/Teff

RSGC1-F11
1,015[15]
L/Teff

W Persei
1,011[9]
L/Teff

LMC 143877
1,010[2]

KW Sagittarii
1,009[3]-1,460[1]
AD & L/Teff
Margin of possible error: ±142 R☉.[3]

RSGC1-F12
1,005[9]
L/Teff

Progenitor of SN 2017eaw
1,000–2,000[38]

Localed in NGC 6946

SMC 46497
990[2]

LMC 140296
990[2]

RSGC1-F09
986[15]
L/Teff

NR Vulpeculae
980[1]
L/Teff

SMC 12322
980[2]

LMC 177997
980[2]

SMC 59803
970[2]

Westerlund 1-20
965[9]
L/Teff

GCIRS 7
960[39]–1,000[40]
AD
At the galactic center. Margin of possible error: ±92 R☉[39] or ±150 R☉.[40]

Betelgeuse (Alpha Orionis)
7002955000000000000♠955±217[41]
AD
Star with the third largest apparent size after R Doradus and the Sun. Other estimates range from 887 ± 203 R☉[42] to 1,180 R☉[43]

SMC 50840
950[2]

J004424.94+412322.3
945–1,300[44]
L/Teff
Located in the Andromeda Galaxy.

RSGC1-F10
931[15]
L/Teff

S Cassiopeiae
930[45][46]

IX Carinae
920[1]
L/Teff

HV 2112
916[47]
L/Teff
Most likely candidate for a Thorne-Zytkow Object.

RSGC1-F07
910[15]
L/Teff

LMC 54365
900[2]

IRAS 04498-6842
900[48]–1,660[16]
L/Teff

NSV 25875
891[27]
L/Teff

LMC 109106
890[2]

RSGC1-F06
885[15]
L/Teff

LMC 116895
880[2]

SMC 30616
880[2]

LMC 64048
880[2]

IRAS 05558-7000
880[16]
L/Teff

V437 Scuti
874[27]
L/Teff

IRAS 04407-7000
870[16]
L/Teff

IRAS 05329-6708
870[16]
L/Teff

V602 Carinae
860[1]–1,050[49]
L/Teff & AD
Margin of possible error: ±165 R☉.[49]

J004047.82+410936.4
860[44]
L/Teff
Localed in the Andromeda Galaxy

J004428.71+420601.6
860[44]
L/Teff
Localed in the Andromeda Galaxy

V669 Cassiopeiae
859[27]
L/Teff

SMC 55681
850[2]

SMC 15510
850[2]

LMC 61753
830[2]

LMC 62090
830[2]

SMC 11709
830[2]

V1185 Scorpii
830[27]
L/Teff

LMC 142199
810[2]

IRAS 05294-7104
810[16]
L/Teff

IRAS 05402-6956
800[16]
L/Teff

LMC 134383
800[2]

Eta Carinae A (Tseen She)
800[50]

Previously thought to be the most massive single star, but in 2005 it was realized to be a binary system. During the Great Eruption, the size was as large as 1,400 R☉.[51]

V441 Persei
799[9]
L/Teff

BU Persei
795[9]
L/Teff

IRAS 05298-6957
790[16]
L/Teff

BO Carinae
790[1]
L/Teff

LMC 142907
790[2]

J004359.94+411330.9
785[44]
L/Teff
Localed in the Andromeda Galaxy

SU Persei
780[1]
L/Teff
In the Perseus Double Cluster

RS Persei
770[52]–1,000[1]
AD & L/Teff
In the Perseus Double Cluster. Margin of possible error: ±30 R☉.[52]

AV Persei
770[1]
L/Teff
In the Perseus Double Cluster

V355 Cephei
770[1]
L/Teff
Mauron et al. 2011 derive 37,000 L☉, which implies a size around 300 R☉.[36]

J004124.80+411634.7
760[44]
L/Teff
Localed in the Andromeda Galaxy

V915 Scorpii
760[53][54]
L/Teff

S Cephei
760[55]
AD

YZ Persei
758[9]
L/Teff

J004447.08+412801.7
755[44]
L/Teff
Localed in the Andromeda Galaxy

GP Cassiopeiae
751[9]
L/Teff

Outer limits of the asteroid belt
750–900

 Reported for reference

SMC 11939
750[2]

HD 303250
750[1]
L/Teff

V382 Carinae
747[56]

The brightest yellow hypergiant in the night sky, one of the rarest types of star. Other estimate ranges of 600 R☉ to 1,100 R☉.[57]

RU Virginis
740[58]
L/Teff

LMC 137818
740[2]

SMC 48122
740[2]

IRAS 04545-7000
730[16]
L/Teff

IRAS 05003-6712
730[16]
L/Teff

SMC 56732
730[2]

KK Persei
724[9]
L/Teff

V648 Cassiopeiae
710[1]
L/Teff

XX Persei
710[9]
L/Teff
Located in the Perseus Double Cluster and near the border with Andromeda.

TV Geminorum
620–710[59] (–770)[1]
L/Teff

HD 179821
704[60]

A yellow hypergiant, although most authors consider it as a supergiant, a protoplanetary nebula or a post-AGB star with a luminosity of only 16,000 L☉.

J004255.95+404857.5
700[44]
L/Teff
Localed in the Andromeda Galaxy

J003950.98+405422.5
700[61]
L/Teff
Localed in the Andromeda Galaxy

LMC 169754
700[2]

LMC 65558
700[2]

V528 Carinae
700[1]
L/Teff

RSGC1-F14
700[15]
L/Teff

The following well-known stars are listed for the purpose of comparison.

V354 Cephei
690[36]-1,520[1]
L/Teff

Antares A (Alpha Scorpii A)
680[62]
AD
This star appears to vary its size by 165 R☉. Older estimates have given radii over 800 R☉,[63][64] but some are likely to have been affected by asymmetry of the atmosphere and the narrow range of infrared wavelengths observed.[62]

HR 5171 Ab
7002650000000000000♠650±150[18]
AD
Companion of HR 5171 A.

CE Tauri
587–593[65] (–608[66])
AD
Second reddest star in the night sky.[22] Can be occulted by the Moon, allowing accurate determination of its apparent diameter.

CW Leonis
500[67]–700[68]
L/Teff
CW Leonis is one of the mistaken identities as the claimed planet "Nibiru" or "Planet X", due to its brightness as it approaches 1st magnitude. Other estimates range from 390 R☉[67] to 826 R☉.[27]

Rho Cassiopeiae
400–500[69]

Yellow hypergiant, one of the rarest types of a star.

R Leporis (Hind's "Crimson Star")
400[70]–535[71]

Margin of possible error: ±90 R☉.[70]

V509 Cassiopeiae
400–900[72]

Yellow hypergiant, one of the rarest types of a star.

Inner limits of the asteroid belt
380

 Reported for reference

V838 Monocerotis
380 (in 2009)[73]

A short time after the outburst V838 Mon was measured at 1,570 ± 400 R☉.[74] However the distance to this "L-type supergiant", and hence its size, have since been reduced and it proved to be a transient object that shrunk about four-fold over a few years. Like CW Leo, it has been erroneously portrayed as "Nibiru" or "Planet X" (see above).

R Doradus
7002370000000000000♠370±50[75]

Star with the second largest apparent size after the Sun.

Tail of Comet Hyakutake
360

Reported for reference

IRC +10420
357[76]–1,342[27]
L/Teff
A yellow hypergiant that has increased its temperature into the LBV range.

The Pistol Star
340[77]

Blue hypergiant, among the most massive and luminous stars known.

Mira A (Omicron Ceti)
332–402[78]
AD
Prototype Mira variable. De beck et al. 2010 calculates 541 R☉.[27]

La Superba (Y Canum Venaticorum)
307[27]–390[79]
L/Teff
Referred to as La Superba by Angelo Secchi. Currently one of the coolest and reddest stars.

Orbit of Mars
297–358

Reported for reference

Alpha Herculis (Ras Algethi)
7002284000000000000♠284±60[80]

The estimate ranges from 264 R☉ to 303 R☉[80]

Sun's red giant phase
256[81]

The core hydrogen would be exhausted in 5.4 billion years. In 7.9 billion years, The Sun would reach the tip of the red-giant branch of the Hertzsprung–Russell diagram. (see below)  Reported for reference

Orbit of Earth
215 (211–219)

Reported for reference

Deneb (Alpha Cygni)
7002203000000000000♠203±17[82]

Prototype Alpha Cygni variable.

Solar System Habitable Zone
200–520[83] (uncertain)

Reported for reference

Orbit of Venus
154–157

Reported for reference

Epsilon Aurigae A (Almaaz)
143–358[84]

ε Aur was incorrectly claimed in 1970 as the largest star with a size between 2,000 R☉ and 3,000 R☉,[85] even though it later turned out not to be an infrared light star but rather a dusk torus surrounding the system.

S Doradus
100–380[86]

Prototype S Doradus variable, even though P Cygni was the first discovered.

Peony Star
92[87]

Candidate for most luminous star in the Milky Way.

Rigel A (Beta Orionis A)
78.9[88]–115[89]

Margin of possible error: ±7.4 R☉.[88]

Canopus (Alpha Carinae)
7001710000000000000♠71±4[90]

Second brightest star in the night sky.

Orbit of Mercury
66–100

Reported for reference

LBV 1806-20
45–145[91]
L/Teff
Formerly a candidate for the most luminous star in the Milky Way with 40 million L☉,[92] but the luminosity has been revised later only 2–5 million L☉.[93][94]

Aldebaran (Alpha Tauri)
7001441300000000000♠44.13±0.84[95]
AD

Polaris (Alpha Ursae Minoris)
37.5[96]

The current northern pole star.

R136a1
28.8[97]–35.4[98]

Also on record as the most massive and luminous star known (265 - 315 M☉ and 8.71 million L☉).

Arcturus (Alpha Boötis)
7001254000000000000♠25.4±0.2[99]

Brightest star in the northern hemisphere.

HDE 226868
20–22[100]

The supergiant companion of black hole Cygnus X-1. The black hole is 500,000 times smaller than the star.

VV Cephei B
13[101]–25[102]

The B-type main sequence companion of VV Cephei A.

Sun's helium burning phase
10

After the red-giant branch the Sun has approximately 120 million years of active life left.  Reported for reference

Sun
1

The largest object in the Solar System.  Reported for reference

text: Jump up ^ AD: radius determined from angular diameter and distanceL/Teff: radius calculated from bolometric luminosity and effective temperature

tag: ol


document_title: Azygos vein

question_text: the azygos vein drains what part of the body

root

text: Azygos vein

text: Structure[edit]

text: The azygos vein transports deoxygenated blood from the posterior walls of the thorax and abdomen into the superior vena cava vein. The anatomy of this blood vessel can be quite variable. In some rare variations for example, it also drains thoracic veins, bronchial veins and even gonadal veins. The vein is so named because it has no symmetrically equivalent vein on the left side of the body.

tag: p

text: It is formed by the union of the ascending lumbar veins with the right subcostal veins at the level of the 12th thoracic vertebra, ascending in the posterior mediastinum, and arching over the right main bronchus posteriorly at the root of the right lung to join the superior vena cava. This "arch of the azygos vein" (arcus venae azygos) is an important anatomic landmark. As an anatomical variation in 1-2% of the population, the arch can be displaced laterally, thereby creating a pleural septum separating an azygos lobe from the upper lobe of the right lung.

text: A major tributary is the hemiazygos vein, a similar structure on the opposite side of the vertebral column. Other tributaries include the bronchial veins, pericardial veins, and posterior right intercostal veins. It communicates with the vertebrael venous plexuses.

text: Function[edit]

text: The azygos system of veins is considered to be the azygos vein, along with its left-sided counterparts, the hemiazygos vein and the accessory hemiazygos vein.

text: Clinical significance[edit]

text: Azygos vein abnormalities can be inferenced on chest radiograph by enlargement of the azygos vein shadow greater than 1 cm. False positives can occur in heart failure causing increased pressures on the right side of the heart, or adjacent lymphadenopathy.[4]

text: History[edit]

text: The Greek root zyg refers to a pair. 'A-' means not. Thus, azygos means unpaired. The azygos vein is unpaired in that there is only one in the body, mostly on the right side. While there is the hemiazygos vein and its accessory on the left side of the body, they are considered tributaries of the azygos vein rather than its left-side equivalent.

text: This terminology is only accurate in some species, such as the human, dog and cat. Ruminants (such as sheep and cows) have paired azygos veins.

text: Additional images[edit]

text:
Diagram showing completion of development of the parietal veins.

The venæ cavæ and azygos veins, with their tributaries.

Mediastinal surface of right lung.

Azygos vein

Azygos vein

tag: ul


document_title: Big One (roller coaster)

question_text: when did the pepsi max big one open

question_tokens: when did the pepsi max big one open

text: Big One (roller coaster)

text: History[edit]

text: The Big One was manufactured by Arrow Dynamics. Construction of the ride began in September 1993 and lasted just over seven months. The tubular track and supports were airlifted from Bolton to Blackpool and stored at nearby Blackpool Airport. During the start of the construction of the ride, the south of Blackpool promenade was closed and pieces of the structure were stored on the road adjacent to the Pleasure Beach. The first pieces to be fitted were the large foundations that would follow on from the main supports. Once all the supports were fitted, the tubular track was fitted followed by additional supports on the turnaround and the mid course brake section. The ride opened to the public on 28 May 1994.

text: Statistics[edit]

text: The ride is the second Megacoaster to be built by Arrow Dynamics, the first being Magnum XL-200 at Cedar Point in Sandusky, Ohio. At its highest point, the ride reaches 235 feet (72 m) above sea level, but only stands 213 feet (65 m) above the ground with the first drop measuring 205 feet (62 m). These numbers were later confirmed by Ron Toomer of Arrow Dynamics.[1] The first drop has an incline angle of 65 degrees and the usual maximum speed for the ride is 74 miles per hour (119 km/h). The ride lasts approximately three minutes and during this time riders normally experience positive g-forces of up to 3.5g and negative g-forces of up to 0.5g. Blackpool Pleasure Beach advertises the ride as rising 235 feet (72 m), but that is above sea level and not the actual height of the ride.

text: The ride is capable of running three trains at any one time. Each train has five cars with six passengers to a car, enabling each train to carry 30 riders two-abreast in total. This gives Big One a capacity of 1,800 people per hour. The colour scheme for each train is the same: a blue base with two coloured bands around the side and front (red and white) showing the Union Jack logo. Each train is numbered at the back of the fifth car, and each car is numbered according to the back of each section. During testing, sand bags are used to weigh the train down. This is a safety mechanism and is common practice on roller coasters of a certain height. Before the ride was granted a certificate to operate, Blackpool Pleasure Beach had to appeal to Blackpool Airport which is one mile from the park. Due to the ride's height, warning beacons had to be installed on the peaks of the first two hills, including the main drop, before the ride was given the all clear to operate.

text: Records[edit]

text: When it opened on 28 May 1994, Big One was both the tallest and steepest roller coaster in the world.[2] It was also one of the longest out-and-back roller coasters, measuring 5,497 feet (1,675 m). With a 205-foot drop and 74 mph top speed, it was second only to Steel Phantom at Kennywood in West Mifflin, Pennsylvania in speed, but it was the fastest coaster in Europe.[2][note 1] The Big One lost its height record to Fujiyama in Japan in 1996, though it remained the tallest and fastest roller coaster in Europe until 2002, when Silver Star opened at Europa-Park in Germany. The ride still remains the tallest in the United Kingdom, although Stealth in Thorpe Park is the fastest. It is also the second longest in the UK, losing only to Lightwater Valley's Ultimate.

text: Richard Rodriguez completed a 112-day endurance record on the roller coaster in 2012. This broke the world record for the most consecutive days on a rollercoaster. This attempt was only during operating hours (approximately six hours a day) as opposed to 24 hours a day. He also had his own row of seating assigned only for him during the record.

text: Incidents[edit]

text: In May 1994 during the ride's inaugural season, 26 people were injured when the computer system failed to completely stop a train returning to the station. The result of this brake failure was a collision with a train parked inside the ride's station.[3] Another train collision occurred in August 2000, caused by another computer failure and injured 16 people.[3]

text: Notes[edit]

text: Jump up ^ When Desperado opened three months later, Big One became the third fastest. Though not standing as tall as Big One, Steel Phantom and Desperado both had longer drops (225 feet) and therefore achieved greater speeds.


document_title: This too shall pass

question_text: where does the phrase this too shall pass come from

text: This too shall pass

text: History[edit]

text: An early English reference to the adage may be in Jane Austen's Pride and Prejudice (Vol. III, Ch. 6), published in 1813. The "philosophic composure" of Mr. Bennet leads him to reply to his daughter, Elizabeth, who has counseled him not to become inconsolable after a recent family misfortune, that "You may well warn me against such an evil. Human nature is so prone to fall into it! ...I am not afraid of being overpowered by the impression. It will pass away soon enough."

text: Another early English citation of "this too shall pass" appears in 1848:

text: When an Eastern sage was desired by his sultan to inscribe on a ring the sentiment which, amidst the perpetual change of human affairs, was most descriptive of their real tendency, he engraved on it the words : — "And this, too, shall pass away." It is impossible to imagine a thought more truly and universally applicable to human affairs than that expressed in these memorable words, or more descriptive of that perpetual oscillation from good to evil, and from evil to good, which from the beginning of the world has been the invariable characteristic of the annals of man, and so evidently flows from the strange mixture of noble and generous with base and selfish inclinations, which is constantly found in the children of Adam.[1]

text: It was also used in 1852, in a retelling of fable, entitled "Solomon's Seal", by the English poet Edward Fitzgerald.[2] In it, a sultan requests of King Solomon a sentence that would always be true in good times or bad; Solomon responds, "This too will pass away".[3] On September 30, 1859, Abraham Lincoln recounted a similar story:

text: It is said an Eastern monarch once charged his wise men to invent him a sentence, to be ever in view, and which should be true and appropriate in all times and situations. They presented him the words: "And this, too, shall pass away." How much it expresses! How chastening in the hour of pride! How consoling in the depths of affliction![4][5]

text: Origin of the fable[edit]

text: The fable retold by Fitzgerald can be traced to the first half of the 19th century, appearing in American papers by at least as early as 1839.[3] It usually involved a nameless "Eastern monarch". Its origin has been traced to the works of Persian Sufi poets, such as Sanai and Attar of Nishapur.[3] Attar records the fable of a powerful king who asks assembled wise men to create a ring that will make him happy when he is sad. After deliberation the sages hand him a simple ring with the words "This too will pass" etched on it, which has the desired effect to make him happy when he is sad. It also, however, became a curse for whenever he is happy.[3]

text: Many versions of comparable stories have been recorded by the Israel Folklore Archive at the University of Haifa.[6] Jewish folklore often casts Solomon as either the king humbled by the adage, or as the one who delivers it to another.

text: In some versions the phrase is simplified even further, appearing as only the Hebrew letters gimel, zayin, and yodh, which begin the words "Gam zeh ya'avor" (Hebrew: גם זה יעבור, gam zeh yaavor), "this too shall pass."


document_title: Bunty Bailey

question_text: who was the girl in the aha video

question_tokens: who was the girl in the aha video

text: Bunty Bailey

text:
Bunty Bailey

Born
Therese Bailey
(1964-05-23) 23 May 1964 (age 54)
England

Occupation
Actress, model

Years active
1980–2008

Website
http://www.myspace.com/buntybailey

tag: table

text: Therese "Bunty" Bailey (born 23 May 1964)[1] is an English model, dancer and actress. Bunty started her career as a dancer in the dance group Hot Gossip in the early 1980s.[2] She became known as the girl in the music videos of A-ha's singles "Take On Me" and "The Sun Always Shines on T.V." made in 1985; she met Morten Harket (the lead-singer and voice of a-ha) on the set and became his girlfriend.

text: She has since appeared in several films, with her most recent role in 2008 as a Gypsy Momma in Defunct. She is currently living in Wraysbury, Berkshire. She did work as a children's dance teacher at Wraysbury and Datchet Village Hall,[2][3] She was listed by Fox News as being one of The Hottest '80s Video Vixens.[4] Bunty has two sons, Jake and Felix Bailey, who were born in 1996 and 1997 respectively.[2] In June 2009, she was one of the first people to take advantage of the UK government car scrappage scheme and was invited to breakfast with the Prime Minister at the time, Gordon Brown.[2] In September 2012, Bailey appeared as the mystery guest on Channel 4's Big Fat Quiz of the '80s, with her appearance in the A-ha videos being the correct answer.[5]

text: Filmography[edit]

text:
The Kenny Everett Show (early 1980s) with Hot Gossip
"Talking Loud and Clear", OMD (1984)
"Take On Me", a-ha (1985) as the Girl
"The Sun Always Shines on TV", a-ha (1985) as the Girl
"To Be a Lover", Billy Idol (1986)
Spellcaster (1987) as Cassandra Castle
Dolls (1987) as Isabel Prange
Rock and the Money-Hungry Party Girls (1988)
Glitch! (1988) as Bimbo
a-ha: Headlines and Deadlines - The Hits of a-ha (1991)
Essential Music Videos: Hits of the 80s (2003)
Video on Trial: "Episode No.2.6" (2006)
Defunct (2008) as Gypsy Momma


document_title: Happy Death Day

question_text: who keeps killing tree in happy death day

text: Happy Death Day

text: Plot[edit]

text: Theresa "Tree" Gelbman wakes up on her birthday on Monday, September 18, 2017 in the dorm room of classmate Carter Davis after a drunken binge the previous evening. Tree goes through the day being self-centered, dismissive, and condescending to her classmates and previous hook-ups, ignoring her father's invitation to a restaurant, throwing away a birthday cupcake given to her by her roommate Lori Spengler, and having an affair with Dr. Gregory Butler, her professor. That night, while going to a party, Tree is lured into a tunnel where she is brutally murdered by a hooded figure wearing a mask of the campus mascot.

text: Tree wakes up the next morning back in Carter's bed with the previous day's events repeating. Unnerved, she relives the day and avoids the tunnel, instead heading to a fraternity house for a surprise party. However, after becoming intimate with her classmate Nick, the masked killer murders him before killing Tree once more. Tree realizes that she is in a time loop and tries to avoid her death by barricading herself in her room. However, she is murdered again when the killer hides in her bedroom.

text: Upon waking up again, she relays her story to Carter, who suggests that she take advantage of the loop in order to figure out who her killer is. She spends the next several iterations trailing suspected classmates and dying each time.

text: After Tree dies from being bludgeoned by a baseball bat, she passes out shortly after waking up. She awakens in the campus hospital where she learns that her body shows evidence of recovery from multiple, massive, traumatic injuries, meaning she has retained damage from her previous murders even after waking up fully healed every time. Tree escapes the hospital room only to be chased by the killer until she manages to flee in Butler's car. While driving, she is pulled over by a police officer and volunteers to be arrested in order to be spared. While held in the officer's squad car, the killer runs over the officer and blows up the squad car by igniting the fuel tank with a candle.

text: Waking up in Carter's bed again, Tree convinces Carter of her predicament by showing that she holds foreknowledge of the day's events. In Corky's, Tree admits to Carter that she does not like who she has become as she is distant from her father in the wake of her mother's death three years ago. Tree catches a local news report on John Tombs, a serial killer who is being held in the hospital on her campus. Concluding that Tombs is her killer, Tree rushes to the hospital to warn of his escape. Tombs breaks free and nearly kills Tree, but Carter follows and rescues her. Tombs snaps Carter's neck before chasing Tree to a nearby bell tower where she manages to subdue him with a crowbar. Realizing that Carter will remain dead if she doesn't restart the loop, Tree hangs herself in the tower.

text: During the next iteration, Tree sets out to be a kinder person by ending her affair with Dr. Butler and meeting with her father to resolve her inner grief. That night, she prepares to stop Tombs. He manages to get the upper hand on her until Tree utilizes a campus-wide blackout that occurs during the loop to disarm him and shoot him to death. Relieved to finally be free, she celebrates her birthday in Carter's room and eats the cupcake given to her by Lori.

text: However, the next morning Tree wakes up again on her birthday. Confused and distraught over the fact that killing Tombs did not stop the time loop, Tree returns to her room where Lori offers the cupcake again. Tree realizes that she had died in her sleep and also notes that this was the only time she had ever eaten the cupcake. Tree realizes that Lori is the true killer; Lori had poisoned the cupcake, but when Tree did not eat it, she utilized her job as a nurse in the hospital to frame Tombs for Tree's murder. Tree tries to coerce Lori to have a bite and when Lori refuses, Tree decides to take it to the police. Lori attacks Tree, locks the door and confesses that she was jealous of her affair with Dr. Butler. Tree manages to stuff the cupcake into Lori's mouth before kicking her out of a window, sending her falling to her death. Tree and Carter muse over the day's events back in the restaurant. He offers her his room for the night, also commenting her situation is a lot like the film Groundhog Day. Tree wakes up the next day believing herself to be in another loop, but it turns out to be a prank by Carter. The two share a kiss.

text: Cast[edit]

text:
Jessica Rothe as Theresa "Tree" Gelbman
Israel Broussard as Carter Davis
Ruby Modine as Lori Spengler
Rachel Matthews as Danielle Bouseman
Charles Aitken as Gregory Butler
Rob Mello as John Tombs
Phi Vu as Ryan Phan
Caleb Spillyards as Tim Bauer
Jason Bayle as David Gelbman
Laura Clifton as Stephanie Butler
Cariella Smith as Becky Shepard
Tran Tran as Emily
Blaine Kern III as Nick Sims
Dane Rhodes as Officer Santora
Tenea Intriago as Student Protestor
Missy Yager as Mrs. Gelbman

text: Production[edit]

text: Pre-production[edit]

text:
"The movie was in pre-production or soft production at the time, and I came on and I loved the concept of the movie. I loved the idea of a girl, trapped in a time loop who has to solve her own murder."

– Director Christopher B. Landon about the concept of the film.[5]

tag: div

text: The film was first announced in July 2007, with Megan Fox attached to star. The film was originally titled Half to Death, produced by Michael Bay and Rogue Pictures, and directed by Antti Jokinen.[6] Christopher B. Landon was hired to rewrite the Scott Lobdell script, and while he liked the reworked script the studio decided to not move on with it. The project was only revived years later, as original producer Angela Mancuso had lunch with Landon and remembered about Half to Death. Landon decided to send the script to Jason Blum of Blumhouse Productions, with whom he had worked in the Paranormal Activity sequels, and he approved it, leading to a green-light by Universal Pictures.[5] Blumhouse announced the project on October 11, 2016, with Landon directing and Jessica Rothe cast in the lead role of the film.[7] On November 8, 2016, it was announced that Ruby Modine, Charles Aitken and Rachel Matthews had joined the cast, alongside Rothe and Israel Broussard.[8] The film got eventually retitled Happy Death Day in June 2017.[9]

text: The mask was constructed by Tony Gardner, the same man who built the "Ghostface" mask from every Scream film, and its design was personal. Landon explains, "During preproduction... I was expecting my first son. I don't know if I just had babies on the brain, or if I was subconsciously scared to become a father, but that baby image was floating around in my head. Tony made us a pig mask, too, but when I wore the baby mask in the office, I scared a co-worker, and we thought... yeah, this is it. This is the one."[10] Scream itself was listed among the influences Christopher Landon took for the film, along with Halloween (1978), Groundhog Day and comedies of the 1980s such as Sixteen Candles and Back to the Future,[11] given he aimed to make a "fun, silly horror movie". He also aimed to emulate the protagonist's personal growth in Groundhog Day to comment on "this age of social media and all the crappy things that kids do to each other."[12]

text: Writing[edit]

text: Writer Scott Lobdell said he wanted to play with the tropes of the slasher genre, as according to him "every slasher film opens up with the mean girl getting killed and the good girl living till the end. And I thought, 'How can I make the mean girl and the good girl the same person?'" [12] In the original draft, Lori and Dr. Butler were the killers together. Landon says, "They were a psycho couple murdering Tree together. That ultimately didn’t work for me. I thought Gregory was a great opportunity to be a suspect. To make him a killer, it didn't help me. That was a change I really wanted to make."[13] Also, in the original draft there was no birthday,[13] and no romance, which Landon added to humanize Tree.[5] Landon decided to shorten the protagonist's name Teresa into Tree, which also conveyed her character arc as "trees need to grow and you see this character go from one person to another".[14]

text: Filming[edit]

text: Filming took place at and around Loyola University in New Orleans, Louisiana,[15] and it lasted 5 weeks.[16] The scenes where Tree awakens in Carter's bed after her death were filmed back to back in a span of two days.[17] The scene after Lori dies was supposed to be at the sorority house, but the filming permit was over before production was able to shoot there, forcing the location to be changed into a Los Angeles diner also featured in another Blumhouse production, Split.[14]

text: Alternate ending[edit]

text: In the original ending of the film, Tree is taken to the hospital after her encounter with Lori. The doctor instructs her to stay away from pain medication for at least a day due to the extent of her injuries. After he leaves, a nurse comes in and tells Tree she is giving Tree something for the pain and Tree informs the nurse of the doctor's orders. The nurse reveals herself to be Dr. Butler's wife Stephanie, who says it is for her pain and then murders Tree in revenge for the affair between her and Dr. Butler.

text: This version was shown in the test screenings for the film, and was received negatively by the audience, forcing the writers to come up with the theatrical ending. Director Christopher Landon also revealed Lori and Dr. Butler were the killers in the rough drafts, which later inspired the idea of the poisoned cupcake.[18]

text: Music[edit]

text:
Happy Death Day (Original Motion Picture Soundtrack)

Soundtrack album by Bear McCreary

Released
October 13, 2017

Genre
Film score

Length
39:57 (Standard album)
44:16 (Bonus track version)

Label
Back Lot Music

text:
Professional ratings

Review scores

Source
Rating

Soundtrack Dreams

text: Bear McCreary is the composer of all tracks.

text:
Standard album[19]

No.
Title
Length

1.
"Day One"
5:26

2.
"Day Two"
6:05

3.
"Day Three"
4:18

4.
"Day Four"
2:17

5.
"Hospital Pursuit"
5:55

6.
"The Bell Tower"
3:30

7.
"Righting Wrongs"
3:40

8.
"Tree Takes Control"
4:30

9.
"The Cupcake"
4:16

Total length:
39:57

text:
Bonus track

No.
Title
Length

10.
"Happy Death Day End Title Credits"
4:19

Total length:
44:16

text: Reception[edit]

text: Box office[edit]

text: Happy Death Day grossed $55.7 million in the United States and Canada, and $67 million in other territories, for a worldwide total of $122.6 million, against a production budget of $4.8 million.[1]

text: In the United States and Canada, Happy Death Day was released alongside Marshall, The Foreigner and Professor Marston and the Wonder Women, and was expected to gross $15–20 million from 3,130 theaters in its opening weekend.[20] It made $1 million from Thursday night previews at 2,450 theaters, similar to fellow Blumhouse release The Visit ($1.05 million in 2015)[21] and $11.6 million on its first day, increasing weekend projections to $26 million. It went on to debut to $26 million, topping the box office, making it the third Blumhouse Productions film of 2017 (after Split and Get Out) to do so.[4] It fell 64% in its second weekend to $9.4 million, finishing in third behind newcomers Boo 2! A Madea Halloween and Geostorm.[22]

text: Critical response[edit]

text: On review aggregator website Rotten Tomatoes, the film has an approval rating of 71% based on 119 reviews, with an average rating of 6/10. The site's critical consensus reads, "Happy Death Day puts a darkly humorous sci-fi spin on slasher conventions, with added edge courtesy of a starmaking performance from Jessica Rothe."[23] On Metacritic, the film has a weighted average score of 57 out of 100, based on 26 critics, indicating "mixed or average reviews".[24] Audiences polled by CinemaScore gave the film an average grade of "B" on an A+ to F scale, while PostTrak reported filmgoers gave it a 52% "definite recommend".[4]

text: Critics noted that although the film makes laudatory attempts at merging genres—including romantic comedy, horror and "campus satire"—the end results were mixed.[3][25] Jamie East from The Sun likened it to a "slasher Mean Girls," while Chris Agar of Screen Rant said that the "fun, if silly, blending of genre tropes...ends up being a double-edged sword."[26][27]

text: Home media[edit]

text: The film was released on digital HD on January 2, 2018 and was released on DVD and Blu-Ray on January 16, 2018. The home release features the original ending.[28]

text: Sequel[edit]

text: Director Christopher B. Landon has talked about the possibility of a sequel, focusing on why Tree went into a time loop.[29] Jessica Rothe stated that while most horror sequels retread the original, Landon's pitch instead "elevates the movie from being a horror movie into a Back to the Future type of genre film where the sequel joins us right from where we left off, it explains a lot of things in the first one that didn’t get explained, and it elevates everything."[30] Filming is scheduled to begin in May 2018.[31] On May 1, 2018, it was announced that Rothe and Israel Broussard will be returning for the sequel, reprising their roles as Tree Gelbman and Carter Davis, respectively. In addition, Suraj Sharma and Sarah Yarkin have been cast.[32]


document_title: International System of Units

question_text: what is the standard unit of length in the si system

question_tokens: what is the standard unit of length in the si system

text: International System of Units

text: History[edit]

text: The metric system was first implemented during the French Revolution (1790s) with just the metre and kilogram as standards of length and mass[Note 1] respectively. In the 1830s Carl Friedrich Gauss laid the foundations for a coherent system based on length, mass, and time. In the 1860s a group working under the auspices of the British Association for the Advancement of Science formulated the requirement for a coherent system of units with base units and derived units. The inclusion of electrical units into the system was hampered by the customary use of more than one set of units, until 1900 when Giovanni Giorgi identified the need to define one single electrical quantity as a fourth base quantity alongside the original three base quantities.

text: Meanwhile, in 1875, the Treaty of the Metre passed responsibility for verification of the kilogram and metre against agreed prototypes from French to international control. In 1921, the Treaty was extended to include all physical quantities including electrical units originally defined in 1893.

text: In 1948, an overhaul of the metric system was set in motion which resulted in the development of the "Practical system of units" which, on its publication in 1960, was given the name "The International System of Units". In 1954, the 10th General Conference on Weights and Measures (CGPM) identified electric current as the fourth base quantity in the practical system of units and added two more base quantities—temperature and luminous intensity—making six base quantities in all. The units associated with these quantities were the metre, kilogram, second, ampere, kelvin and candela. In 1971, a seventh base quantity, amount of substance represented by the mole, was added to the definition of SI.

text: Early development[edit]

text: The metric system was developed from 1791 onwards by a committee of the French Academy of Sciences, commissioned by the National Assembly and Louis XVI to create a unified and rational system of measures.[5] The group, which included Antoine Lavoisier (the "father of modern chemistry") and the mathematicians Pierre-Simon Laplace and Adrien-Marie Legendre,[6]:89 used the same principles for relating length, volume, and mass that had been proposed by the English clergyman John Wilkins in 1668[7][8] and the concept of using the Earth's meridian as the basis of the definition of length, originally proposed in 1670 by the French abbot Mouton.[9][10]

text: On 30 March 1791, the Assembly adopted the committee's proposed principles for the new decimal system of measure and authorised a survey between Dunkirk and Barcelona to establish the length of the meridian. On 11 July 1792, the committee proposed the names metre, are, litre and grave for the units of length, area, capacity, and mass, respectively. The committee also proposed that multiples and submultiples of these units were to be denoted by decimal-based prefixes such as centi for a hundredth and kilo for a thousand.[11]:82

text: The law of 7 April 1795 (loi du 18 germinal) defined the terms gramme and kilogramme, which replaced the former terms gravet (correctly milligrave) and grave, and on 22 June 1799 (after Pierre Méchain and Jean-Baptiste Delambre had completed the meridian survey) the definitive standard mètre des Archives and kilogramme des Archives were deposited in the French National Archives. On 10 December 1799 (a month after Napoleon's coup d'état), the law by which the metric system was to be definitively adopted in France (loi du 19 frimaire[17]) was passed.[18]

text: During the first half of the nineteenth century there was little consistency in the choice of preferred multiples of the base units – typically the myriametre (7004100000000000000♠10000 metres) was in widespread use in both France and parts of Germany, while the kilogram (7003100000000000000♠1000 grams) rather than the myriagram was used for mass.[3]

text: In 1832, the German mathematician Carl Friedrich Gauss, assisted by Wilhelm Weber, implicitly defined the second as a base unit when he quoted the earth's magnetic field in terms of millimetres, grams, and seconds.[12] Prior to this, the strength of the earth's magnetic field had only been described in relative terms. The technique used by Gauss was to equate the torque induced on a suspended magnet of known mass by the earth's magnetic field with the torque induced on an equivalent system under gravity. The resultant calculations enabled him to assign dimensions based on mass, length and time to the magnetic field.[19]

text: In the 1860s, James Clerk Maxwell, William Thomson (later Lord Kelvin) and others working under the auspices of the British Association for the Advancement of Science, built on Gauss' work and formalised the concept of a coherent system of units with base units and derived units. The principle of coherence was successfully used to define a number of units of measure based on the centimetre–gram–second system of units (CGS), including the erg for energy, the dyne for force, the barye for pressure, the poise for dynamic viscosity and the stokes for kinematic viscosity.[15]

text: Metre Convention[edit]

text:
CGPM vocabulary

French
English
Pages[20]

étalons
[Technical] standard
5, 95

prototype
prototype [kilogram/metre]
5,95

noms spéciaux
[Some derived units have]
special names
16,106

mise en pratique
mise en pratique
[Practical realisation][Note 2]
82, 171

text: A French-inspired initiative for international cooperation in metrology led to the signing in 1875 of the Metre Convention.[6]:353–354 Initially the convention only covered standards for the metre and the kilogram. A set of 30 prototypes of the metre and 40 prototypes of the kilogram,[Note 3] in each case made of a 90% platinum-10% iridium alloy, were manufactured by the British firm Johnson, Matthey & Co and accepted by the CGPM in 1889. One of each was selected at random to become the International prototype metre and International prototype kilogram that replaced the mètre des Archives and kilogramme des Archives respectively. Each member state was entitled to one of each of the remaining prototypes to serve as the national prototype for that country.[21]

text: The treaty established three international organisations to oversee the keeping of international standards of measurement:[22]

text:
General Conference on Weights and Measures (Conférence générale des poids et mesures or CGPM) – a meeting every four to six years of delegates from all member states that receives and discusses a report from the CIPM and that endorses new developments in the SI on the advice of the CIPM.
International Committee for Weights and Measures (Comité international des poids et mesures or CIPM) – a committee that meets annually at the BIPM and is made up of eighteen individuals of high scientific standing, nominated by the CGPM to advise the CGPM on administrative and technical matters
International Bureau of Weights and Measures (Bureau international des poids et mesures or BIPM) – an international metrology centre at Sèvres in France that has custody of the International prototype kilogram, provides metrology services for the CGPM and CIPM, houses the secretariat for these organisations and hosts their formal meetings. Initially its prime metrological purpose was a periodic recalibration of national prototype metres and kilograms against the international prototype.

text: In 1921, the Metre Convention was extended to include all physical units, including the ampere and others defined by the Fourth International Conference of Electricians in Chicago in 1893, thereby enabling the CGPM to address inconsistencies in the way that the metric system had been used.[13][20]:96

text: The official language of the Metre Convention is French[23] and the definitive version of all official documents published by or on behalf of the CGPM is the French-language version.[20]:94

text: Towards the SI[edit]

text: At the close of the 19th century three different systems of units of measure existed for electrical measurements: a CGS-based system for electrostatic units, also known as the Gaussian or ESU system, a CGS-based system for electromechanical units (EMU) and an MKS-based system ("international system")[24] for electrical distribution systems. Attempts to resolve the electrical units in terms of length, mass, and time using dimensional analysis was beset with difficulties—the dimensions depended on whether one used the ESU or EMU systems.[16] This anomaly was resolved in 1900 when Giovanni Giorgi published a paper in which he advocated using a fourth base unit alongside the existing three base units. The fourth unit could be chosen to be electric current, voltage, or electrical resistance.[25]

text: In the late 19th and early 20th centuries, a number of non-coherent units of measure based on the gram/kilogram, the centimetre/metre, and the second, such as the Pferdestärke (metric horsepower) for power,[26][Note 4] the darcy for permeability[27] and the use of "millimetres of mercury" for the measurement of both barometric and blood pressure were developed or propagated, some of which incorporated standard gravity in their definitions.

text: At the end of the Second World War, a number of different systems of measurement were in use throughout the world. Some of these systems were metric system variations, whereas others were based on customary systems of measure. In 1948, after representations by the International Union of Pure and Applied Physics (IUPAP) and by the French Government, the 9th General Conference on Weights and Measures (CGPM) asked the International Committee for Weights and Measures (CIPM) to conduct an international study of the measurement needs of the scientific, technical, and educational communities and "to make recommendations for a single practical system of units of measurement, suitable for adoption by all countries adhering to the Metre Convention".[28]

text: On the basis of the findings of this study, the 10th CGPM in 1954 decided that an international system should be derived from six base units to provide for the measurement of temperature and optical radiation in addition to mechanical and electromagnetic quantities. Six base units were recommended: the metre, kilogram, second, ampere, degree Kelvin (later renamed kelvin), and candela. In 1960, the 11th CGPM named the system the International System of Units, abbreviated SI from the French name, Le Système International d'Unités.[20]:110[29] The BIPM has also described SI as "the modern metric system".[20]:95 The seventh base unit, the mole, was added in 1971 by the 14th CGPM.[30]

text: International System of Quantities[edit]

text: The International System of Quantities (ISQ) is a system based on seven base quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity. Other quantities such as area, pressure, and electrical resistance are derived from these base quantities by clear non-contradictory equations. The ISQ defines the quantities that are measured with the SI units.[31] The ISQ is defined in the international standard ISO/IEC 80000, and was finalised in 2009 with the publication of ISO 80000-1.[32]

text: SI Brochure and conversion factors[edit]

text: The CGPM publishes a brochure which defines and presents SI.[20] Its official version is in French, in line with the Metre Convention.[20]:102 It leaves some scope for local interpretation, particularly regarding names and terms in different languages, so for example the United States' National Institute of Standards and Technology (NIST) has produced a version of the CGPM document (NIST SP 330) which clarifies local interpretation for English-language publications that use American English[33] and another document (NIST SP 811) that gives general guidance for the use of SI in the United States and conversion factors between SI and customary units.[34]

text: The writing and maintenance of the CGPM brochure is carried out by one of the committees of the International Committee for Weights and Measures (CIPM), the Consultative Committee for Units (CCU). The CIPM nominates the chairman of this committee, but the committee includes representatives of various other international bodies rather than CIPM or CGPM nominees.[35][Note 5] This committee thus provides a forum for the bodies concerned to provide input to the CIPM in respect of ongoing enhancements to SI.

text: The definitions of the terms "quantity", "unit", "dimension" etc. that are used in the SI Brochure are those given in the International vocabulary of metrology, a publication produced by the Joint Committee for Guides in Metrology (JCGM), a working group consisting of eight international standards organisations under the chairmanship of the director of the BIPM.[36] The quantities and equations that define the SI units are now referred to as the International System of Quantities (ISQ), and are set out in the International Standard ISO/IEC 80000 Quantities and Units.

text: Units and prefixes[edit]

text: The International System of Units consists of a set of base units, a set of derived units with special names, and a set of decimal-based multipliers that are used as prefixes. The term SI Units covers all three categories, but the term coherent SI units includes only base units and coherent derived units.[20]:103–106

text: Base units[edit]

text: The SI base units are the building blocks of the system and all other units are derived from them. When Maxwell first introduced the concept of a coherent system, he identified three quantities that could be used as base units: mass, length and time. Giorgi later identified the need for an electrical base unit. Theoretically any one of electric current, potential difference, electrical resistance, electrical charge or a number of other quantities could have provided the base unit, with the remaining units then being defined by the laws of physics. In the event, the unit of electric current was chosen for SI. Another three base units (for temperature, substance and luminous intensity) were added later.

text:
SI base units[33]:23[37][38]

Unit
name
Unit
symbol
Quantity
name
Definition (incomplete)[n 1]
Dimension
symbol

metre
m
length

Original (1793): 1/7007100000000000000♠10000000 of the meridian through Paris between the North Pole and the Equator.FG
Interim (1960): 7006165076373000000♠1650763.73 wavelengths in a vacuum of the radiation corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom.
Current (1983): The distance travelled by light in a vacuum in 1/7008299792458000000♠299792458 second.

L

kilogram[n 2]
kg
mass

Original (1793): The grave was defined as being the weight [mass] of one cubic decimetre of pure water at its freezing point.FG
Current (1889): The mass of the International Prototype Kilogram (Le Grand K).[39]

M

second
s
time

Original (Medieval): 1/7004864000000000000♠86400 of a day.
Interim (1956): 1/7007315569259747000♠31556925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time.
Current (1967): The duration of 7009919263177000000♠9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

T

ampere
A
electric current

Original (1881): A tenth of the electromagnetic CGS unit of current. The [CGS] electromagnetic unit of current is that current, flowing in an arc 1 cm long of a circle 1 cm in radius, that creates a field of one oersted at the centre.[40] IEC
Current (1946): The constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 6993200000000000000♠2×10−7 newtons per metre of length.

I

kelvin
K
thermodynamic temperature

Original (1743): The centigrade scale is obtained by assigning 0 °C to the freezing point of water and 100 °C to the boiling point of water.
Interim (1954): The triple point of water (0.01 °C) defined to be exactly 273.16 K.[n 3]
Current (1967): 1/273.16 of the thermodynamic temperature of the triple point of water

Θ

mole
mol
amount of substance

Original (1900): The molecular weight of a substance in mass grams.ICAW
Current (1967): The amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12.[n 4]

N

candela
cd
luminous intensity

Original (1946): The value of the new candle is such that the brightness of the full radiator at the temperature of solidification of platinum is 60 new candles per square centimetre.
Current (1979): The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 7014540000000000000♠5.4×1014 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

J

Note

Jump up ^ Interim definitions are given here only when there has been a significant difference in the definition.
Jump up ^ Despite the prefix "kilo-", the kilogram is the base unit of mass. The kilogram, not the gram, is used in the definitions of derived units. Nonetheless, units of mass are named as if the gram were the base unit.
Jump up ^ In 1954 the unit of thermodynamic temperature was known as the "degree Kelvin" (symbol °K; "Kelvin" spelt with an upper-case "K"). It was renamed the "kelvin" (symbol "K"; "kelvin" spelt with a lower case "k") in 1967.
Jump up ^ When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.

The original definitions of the various base units in the above table were made by the following authorities:

FG = French Government
IEC = International Electrotechnical Commission
ICAW = International Committee on Atomic Weights

All other definitions result from resolutions by either CGPM or the CIPM and are catalogued in the SI Brochure.

text: Derived units[edit]

text: The derived units in the SI are formed by powers, products or quotients of the base units and are unlimited in number.[20]:103[33]:3 Derived units are associated with derived quantities, for example velocity is a quantity that is derived from the base quantities of time and length, so in SI the derived unit is metres per second (symbol m/s). The dimensions of derived units can be expressed in terms of the dimensions of the base units.

text: Coherent units are derived units that contain no numerical factor other than 1—quantities such as standard gravity and density of water are absent from their definitions. In the example above, one newton is the force required to accelerate a mass of one kilogram by one metre per second squared. Since the SI units of mass and acceleration are kg and m·s−2 respectively and F ∝ m × a, the units of force (and hence of newtons) is formed by multiplication to give kg·m·s−2. Since the newton is part of a coherent set of units, the constant of proportionality is 1.

text: For the sake of convenience, some derived units have special names and symbols.[14] Such units may themselves be used in combination with the names and symbols for base units and for other derived units to express the units of other derived quantities. For example, the SI unit of force is the newton (N), the SI unit of pressure is the pascal (Pa)—and the pascal can be defined as one newton per square metre (N/m2).[41]

text:
Named units derived from SI base units[33]:3

Name
Symbol
Quantity
Expressed in
terms of
other SI units
Expressed in
terms of
SI base units

radian
rad
angle

m·m−1

steradian
sr
solid angle

m2·m−2

hertz
Hz
frequency

s−1

newton
N
force, weight

kg·m·s−2

pascal
Pa
pressure, stress
N/m2
kg·m−1·s−2

joule
J
energy, work, heat
N·m
kg·m2·s−2

watt
W
power, radiant flux
J/s
kg·m2·s−3

coulomb
C
electric charge or quantity of electricity

s·A

volt
V
voltage (electrical potential difference), electromotive force
W/A
kg·m2·s−3·A−1

farad
F
capacitance
C/V
kg−1·m−2·s4·A2

ohm
Ω
electrical resistance, impedance, reactance
V/A
kg·m2·s−3·A−2

siemens
S
electrical conductance
A/V
kg−1·m−2·s3·A2

weber
Wb
magnetic flux
V·s
kg·m2·s−2·A−1

tesla
T
magnetic flux density
Wb/m2
kg·s−2·A−1

henry
H
inductance
Wb/A
kg·m2·s−2·A−2

degree Celsius
°C
temperature relative to 273.15 K

K

lumen
lm
luminous flux
cd·sr
cd

lux
lx
illuminance
lm/m2
m−2·cd

becquerel
Bq
radioactivity (decays per unit time)

s−1

gray
Gy
absorbed dose (of ionizing radiation)
J/kg
m2·s−2

sievert
Sv
equivalent dose (of ionizing radiation)
J/kg
m2·s−2

katal
kat
catalytic activity

mol·s−1

Notes
1. The radian and steradian, once given special status, are now considered dimensionless derived units.[33]:3
2. The ordering of this table is such that any derived unit is based only on base units or derived units that precede it in the table.

text: Prefixes[edit]

text: Prefixes are added to unit names to produce multiple and sub-multiples of the original unit. All multiples are integer powers of ten, and above a hundred or below a hundredth all are integer powers of a thousand. For example, kilo- denotes a multiple of a thousand and milli- denotes a multiple of a thousandth, so there are one thousand millimetres to the metre and one thousand metres to the kilometre. The prefixes are never combined, so for example a millionth of a metre is a micrometre, not a millimillimetre. Multiples of the kilogram are named as if the gram were the base unit, so a millionth of a kilogram is a milligram, not a microkilogram.[20]:122[34]:14

text:
v
t
e

text:
Standard prefixes for the SI units of measure

Multiples
Prefix name

deca
hecto
kilo
mega
giga
tera
peta
exa
zetta
yotta

Prefix symbol

da
h
k
M
G
T
P
E
Z
Y

Factor
100
101
102
103
106
109
1012
1015
1018
1021
1024

Fractions
Prefix name

deci
centi
milli
micro
nano
pico
femto
atto
zepto
yocto

Prefix symbol

d
c
m
μ
n
p
f
a
z
y

Factor
100
10−1
10−2
10−3
10−6
10−9
10−12
10−15
10−18
10−21
10−24

text: Non-SI units accepted for use with SI[edit]

text: The SI is capable of measurement of any physical quantity, but many non-SI units still appear in the scientific, technical, and commercial literature, and will continue to be used for many years. Some units are so deeply embedded in history and many cultures that they will continue to be used for the foreseeable future. The CIPM recognized and acknowledged such traditions by compiling a list of non-SI units accepted for use with SI, which are grouped as follows:[20]:123–129[34]:7–11[Note 6]

text: Non-SI units accepted for use with the SI (Table 6):

text: Non-SI units whose values in SI units must be obtained experimentally (Table 7).

text: Other non-SI units (Table 8):

text: Non-SI units associated with the CGS and the CGS-Gaussian system of units (Table 9)

text: Writing unit symbols and the values of quantities [edit]

text: Before 1948, the use and representation of metric quantities was inconsistent and ambiguous.[citation needed] In 1879, the CIPM published recommendations for writing the symbols for length, area, volume and mass, but it was outside its domain to publish recommendations for other quantities. Beginning in about 1900, physicists who had been using the symbol "μ" for "micrometre" (or "micron"), "λ" for "microlitre", and "γ" for "microgram" started to use the symbols "μm", "μL" and "μg", but it was only in 1935, a decade after the revision of the Metre Convention that the CIPM formally adopted this proposal and recommended that the symbol "μ" be used universally as a prefix for 6994100000000000000♠10−6.[42]

text: In 1948, the ninth CGPM approved the first formal recommendation for the writing of symbols in the metric system when the basis of the rules as they are now known was laid down.[43] These rules were subsequently extended by International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) and now cover unit symbols and names, prefix symbols and names, how quantity symbols should be written and used and how the values of quantities should be expressed.[20]:104,130 Both ISO and the IEC have published rules for the presentation of SI units that are generally compatible with those published in the SI Brochure.[44] As of August 2013[update] ISO and IEC were in the process of merging their standards for quantities and units into a single set of compatible documents identified as the ISO/IEC 80000 Standard. The rules covering printing of quantities and units are part of ISO 80000-1:2009.[45]

text: Unit names[edit]

text: Names of units follow the grammatical rules associated with common nouns: in English and in French they start with a lowercase letter (e.g., newton, hertz, pascal), even when the symbol for the unit begins with a capital letter. This also applies to "degrees Celsius", since "degree" is the unit.[46][47] In German, however, the names of units, as with all German nouns, start with capital letters.[48] The spelling of unit names is a matter for the guardians[Note 8] of the language concerned – the official British and American spellings for certain SI units differ – British English, as well as Australian, Canadian and New Zealand English, uses the spelling deca-, metre, and litre whereas American English uses the spelling deka-, meter, and liter, respectively.[33]:3

text: Likewise, the plural forms of units follow the grammar of the language concerned: in English, the normal rules of English grammar are used, e.g. "henries" is the plural of "henry".[49][34]:31 However, the units lux, hertz, and siemens have irregular plurals in that they remain the same in both their singular and plural form. Plural forms can be even more complicated in other languages. For example, in Polish the plural form depends on the actual quantity: 0 metrów, 1 metr, 2 metry, 3 metry, 4 metry, 5 metrów, 6 metrów, 7 metrów, 8 metrów, etc. For fractions it is metrów, e.g., 0,67 metrów, 2,45 metrów.

text: In English, when unit names are combined to denote multiplication of the units concerned, they are separated with a hyphen or a space (e.g. newton-metre or newton metre). The plural is formed by converting the last unit name to the plural form (e.g. ten newton-metres).

text: Unit names as adjectives[edit]

text: A space between the number and the unit symbol (i.e., no hyphen) is specified when the combination is used as an adjective, e.g. "a 25 kg sphere".[20]:133 However, in English a hyphen would be used as normal in this context if the unit name is spelt out, e.g. "a 25-kilogram sphere".[20]:133[50]

text: Chinese and Japanese[edit]

text: Chinese uses traditional logograms for writing the unit names, while in Japanese unit names are written in the phonetic katakana script; in both cases, symbols are also written using the internationally recognised Latin and Greek characters.

text: The basic Chinese units are metre (米 mǐ), litre (升 shēng), gram (克 kè), and second (秒 miǎo), while others include watt (瓦 wǎ). Prefixes include deci- (分 fēn), centi- (厘 lí), milli- (毫 háo), micro- (微 wēi), kilo- (千 qiān), and mega- (兆 zhào). These are combined to form disyllabic characters, such as 厘米 límǐ "centimetre" or 千瓦 qiānwǎ "kilowatt".[51] In the 19th century, various compound characters were also used, similar to Japanese, either imported or formed on the same principles, such as 瓩 for 千瓦 qiānwǎ (kilowatt) or 糎 for 厘米. These are generally not used today, but are occasionally found in older or technical writing.[52]

text: Some units have different names in Taiwan. Meter (公尺), centimeter (公分), liter (公升), kilogram (公斤), gram (公克) and hectare (公頃) have the prefix "公", which means "universal". The prefixes "兆", "分" and "厘" are not commonly used, and the use of "千" is limited to kilowatt (千瓦).

text: A set of characters representing various metric units was created in Japan in the late 19th century. Characters, which are the same in Chinese, exist for three base units: the metre (米), litre (升) and gram (瓦). These were combined with a set of six prefix characters – kilo- (千), hecto- (百), deca- (十), deci- (分), centi- (厘) and milli- (毛) – to form an additional 18 single-character units. The seven length units (kilometre to millimetre), for example, are 粁, 粨, 籵, 米, 粉, 糎 and 粍. These characters, however, are not in common use today; instead, units are written in katakana, the Japanese syllabary used for foreign borrowings, such as キロメートル (kiromētoru) for kilometre, but are also written in standard prefixes such as "km" for kilometre. A few Sino-Japanese words for these units remain in use in Japanese, most significantly "平米" (heibei) for "square metre", but otherwise borrowed pronunciations are used.

text: These characters are examples of the rare phenomenon of single-character loan words – a foreign word represented by a single Japanese character – and form the plurality of such words. Similar characters were also coined for other units, such as British units, though these also have fallen out of use; see Single character gairaigo: Metric units and Single character gairaigo: Other units for a full list.

text: Unit symbols and the values of quantities [edit]

text: Although the writing of unit names is language-specific, the writing of unit symbols and the values of quantities is consistent across all languages and therefore the SI Brochure has specific rules in respect of writing them.[20]:130–135 The guideline produced by the National Institute of Standards and Technology (NIST)[53] clarifies language-specific areas in respect of American English that were left open by the SI Brochure, but is otherwise identical to the SI Brochure.[49]

text: General rules[edit]

text: General rules[Note 9] for writing SI units and quantities apply to text that is either handwritten or produced using an automated process:

text:
The value of a quantity is written as a number followed by a space (representing a multiplication sign) and a unit symbol; e.g., 2.21 kg, 7002730000000000000♠7.3×102 m2, 22 K. This rule explicitly includes the percent sign (%)[20]:134 and the symbol for degrees of temperature (°C).[20]: 133 Exceptions are the symbols for plane angular degrees, minutes, and seconds (°, ′, and ″), which are placed immediately after the number with no intervening space.
Symbols are mathematical entities, not abbreviations, and as such do not have an appended period/full stop (.), unless the rules of grammar demand one for another reason, such as denoting the end of a sentence.
A prefix is part of the unit, and its symbol is prepended to the unit symbol without a separator (e.g., k in km, M in MPa, G in GHz). Compound prefixes are not allowed.
Symbols for derived units formed by multiplication are joined with a centre dot (·) or a non-breaking space; e.g., N·m or N m.
Symbols for derived units formed by division are joined with a solidus (/), or given as a negative exponent. E.g., the "metre per second" can be written m/s, m s−1, m·s−1, or m/s. Only one solidus should be used; e.g., kg/(m·s2) and kg·m−1·s−2 are acceptable, but kg/m/s2 is ambiguous and unacceptable.

text:
The first letter of symbols for units derived from the name of a person is written in upper case; otherwise, they are written in lower case. E.g., the unit of pressure is named after Blaise Pascal, so its symbol is written "Pa", but the symbol for mole is written "mol". Thus, "T" is the symbol for tesla, a measure of magnetic field strength, and "t" the symbol for tonne, a measure of mass. Since 1979, the litre may exceptionally be written using either an uppercase "L" or a lowercase "l", a decision prompted by the similarity of the lowercase letter "l" to the numeral "1", especially with certain typefaces or English-style handwriting. The American NIST recommends that within the United States "L" be used rather than "l".
Symbols of units do not have a plural form; e.g., 25 kg, not 25 kgs.
Uppercase and lowercase prefixes are not interchangeable. E.g., the quantities 1 mW and 1 MW represent two different quantities; the former is the typical power requirement of a hearing aid (1 milliwatt or 0.001 watts), and the latter the typical power requirement of a suburban train (1 megawatt or 7006100000000000000♠1000000 watts).
The 10th resolution of CGPM in 2003 declared that "the symbol for the decimal marker shall be either the point on the line or the comma on the line." In practice, the decimal point is used in English-speaking countries and most of Asia, and the comma in most of Latin America and in continental European countries.[54]
Spaces should be used as a thousands separator (7006100000000000000♠1000000) in contrast to commas or periods (1,000,000 or 1.000.000) to reduce confusion resulting from the variation between these forms in different countries.
Any line-break inside a number, inside a compound unit, or between number and unit should be avoided. Where this is not possible, line breaks should coincide with thousands separators.
Since the value of "billion" and "trillion" can vary from language to language, the dimensionless terms "ppb" (parts per billion) and "ppt" (parts per trillion) should be avoided. No alternative is suggested in the SI Brochure.

text: Printing SI symbols[edit]

text: Further rules[Note 9] are specified in respect of production of text using printing presses, word processors, typewriters and the like.

text:
Symbols are written in upright (Roman) type (m for metres, s for seconds), so as to differentiate from the italic type used for quantities (m for mass, s for displacement). By consensus of international standards bodies, this rule is applied independent of the font used for surrounding text.
In Chinese, Japanese, and Korean language computing (CJK), some of the commonly used units, prefix–unit combinations, or unit–exponent combinations have been allocated predefined single characters taking up a full square. Unicode includes these in its CJK Compatibility[55] and letter-like symbols[56] sub-ranges for back compatibility, without necessarily recommending future usage. These are summarised in Unicode symbols. The cursive ℓ, a letter-like symbol, has been used in a number of countries in addition to China and Japan as a symbol for the litre, but this is not currently recommended by any standards body.
In print, the space used as a thousands separator (commonly called a thin space) is typically narrower than that used between words.

text: Realisation of units[edit]

text: Metrologists carefully distinguish between the definition of a unit and its realisation. The definition of each base unit of the SI is drawn up so that it is unique and provides a sound theoretical basis on which the most accurate and reproducible measurements can be made. The realisation of the definition of a unit is the procedure by which the definition may be used to establish the value and associated uncertainty of a quantity of the same kind as the unit. A description of the mise en pratique[Note 10] of the base units is given in an electronic appendix to the SI Brochure.[58][20]:168–169

text: The published mise en pratique is not the only way in which a base unit can be determined: the SI Brochure states that "any method consistent with the laws of physics could be used to realise any SI unit."[20]:111 In the current (2016) exercise to overhaul the definitions of the base units, various consultative committees of the CIPM have required that more than one mise en pratique shall be developed for determining the value of each unit.[citation needed] In particular:

text:
At least three separate experiments be carried out yielding values having a relative standard uncertainty in the determination of the kilogram of no more than 6992500000000000000♠5×10−8 and at least one of these values should be better than 6992200000000000000♠2×10−8. Both the Watt balance and the Avogadro project should be included in the experiments and any differences between these be reconciled.[59][60]
When the kelvin is being determined, the relative uncertainty of the Boltzmann constant derived from two fundamentally different methods such as acoustic gas thermometry and dielectric constant gas thermometry be better than one part in 6994100000000000000♠10−6 and that these values be corroborated by other measurements.[61]

text: Post-1960 changes[edit]

text: The preamble to the Metre Convention read "Desiring the international uniformity and precision in standards of weight and measure, have resolved to conclude a convention ...".[23] Changing technology has led to an evolution of the definitions and standards that has followed two principal strands – changes to SI itself and clarification of how to use units of measure that are not part of SI, but are still nevertheless used on a worldwide basis.

text: Changes to the SI[edit]

text: Since 1960 the CGPM has made a number of changes to SI. These include:

text:
The 13th CGPM (1967) renamed the "degree Kelvin" (symbol °K) to the "kelvin" (symbol K)[20]:156
The 14th CGPM (1971) added the mole (symbol mol) to the list of base units.[62]
The 14th GCPM (1971) added the pascal (symbol Pa) for pressure and the siemens (symbol S) for electrical conductance to the list of named derived units.[20]:156
The 15th CGPM (1975) added the becquerel (symbol Bq) for "activity referred to a radionuclide" and the gray (symbol Gy) for ionizing radiation to the list of named derived units[20]:156
In order to distinguish between "absorbed dose" and "dose equivalent", the 16th CGPM (1979) added the sievert (symbol Sv) to the list of named derived units as the unit of dose equivalent.[20]:158
The 16th CGPM (1979) clarified that in a break with convention either the letter "L" or the letter "l" may be used as a symbol for the litre, in order to avoid the risk of confusion between the lower-case letter and the number 1.[20]:159

text:
The 21st CGPM (1999) added the katal (symbol kat) for catalytic activity to the list of named derived units.[20]:165
In its original form (1960), the SI defined prefixes for values ranging from pico- (symbol p) having a value of 10−12 to tera- (symbol T) having a value of 1012. The list was extended at the 12th CGPM (1964),[20]:152 at the 15th CGPM (1975)[20]:158 and at the 19th CGPM (1991)[20]:164 to give the current range of prefixes.

text: In addition, advantage was taken of developments in technology to redefine many of the base units enabling the use of higher precision techniques.

text: Retention of non-SI units[edit]

text: Although, in theory, SI can be used for any physical measurement, it is recognised that some non-SI units still appear in the scientific, technical and commercial literature, and will continue to be used for many years to come. In addition, certain other units are so deeply embedded in the history and culture of the human race that they will continue to be used for the foreseeable future.[63] The CIPM has catalogued such units and included them in the SI Brochure so that they can be used consistently.

text: The first such group comprises the units of time and of angles and certain legacy non-SI metric units. Most of mankind has used the day and its subdivisions as a basis of time with the result that the second, minute, hour and day, unlike the foot or the pound, were the same regardless of where it was being measured. The second has been catalogued as an SI unit, its multiples as units of measure that may be used alongside the SI. The measurement of angles has likewise had a long history of consistent use – the radian, being 1/2π of a revolution, has mathematical niceties, but it is cumbersome for navigation, hence the retention of the degree, minute and second of arc. The tonne, litre and hectare were adopted by the CGPM in 1879 and have been retained as units that may be used alongside SI units, having been given unique symbols.

text: Physicists often use units of measure that are based on natural phenomena such as the speed of light, the mass of a proton (approximately one dalton), the charge of an electron and the like. These too have been catalogued in the SI Brochure with consistent symbols, but with the caveat that their physical values need to be measured.[Note 11]

text: In the interests of standardising health-related units of measure used in the nuclear industry, the 12th CGPM (1964) accepted the continued use of the curie (symbol Ci) as a non-SI unit of activity for radionuclides;[20]: 152 the becquerel, sievert and gray were adopted in later years. Similarly, the millimetre of mercury (symbol mmHg) was retained for measuring blood pressure.[20]:127

text: Global adoption[edit]

text: SI has become the world's most widely used system of measurement, used in both everyday commerce and science.[65][66] The change to SI had little effect on everyday life in countries that used the metric system – the metre, kilogram, litre and second remained unchanged as did the way in which they were used – most of the changes only affected measurements in the workplace.[67] The CGPM has a role of recommending changes, but no formal role in the enforcement of such changes—another inter-governmental organisation, the International Organization of Legal Metrology (OIML) provides a forum for harmonisation of national standards and legislation in respect of metrology.

text: Both the degree and rate of adoption of SI varied from country to country—countries that had not adopted the metric system by 1960 and subsequently adopted SI did so directly as part of their metrication programs while others migrated from the CGS system of units to SI. In 1960, the world's largest economy was that of the United States, followed by the Soviet Union (although an accurate estimate of 1960 GDP for this country is not available), West Germany, France, Japan, China and India.[68] The United States and the United Kingdom were non-metric, Soviet Union was metric, France and Germany had been using the metric system for about a century, and China had been using the metric system for 35 years, while India and Japan had adopted the metric system within the preceding five years. Other non-metric countries were those where the United Kingdom or the United States had considerable influence.[Note 12][69] These differences are brought out in the examples below:

text: United Kingdom and the former British Empire[edit]

text: Even though the use of metric units was legalised for trade in the UK in 1864, the UK had signed the Metre Convention in 1884 and the UK Parliament had defined the yard and the pound in terms of the metre and the kilogram in 1897, the UK continued to use the imperial system of measure[70] and to export the imperial system of units to the Empire. In 1932, the system of Imperial Preference was set up at the Ottawa Conference. Although Ireland left the Commonwealth in 1948 and South Africa in 1961,[71] both continued their close economic ties with the Commonwealth.[72]

text: When the SI standard was published in 1960, the only major Commonwealth country to have adopted the metric system was India. In 1863, the first reading of a bill that would have made the metric system compulsory passed its first reading in the House of Commons by 110 votes to 75. The bill, however, failed to make the statute book because of lack of parliamentary time.[11]:136 In 1965, after this and similar false starts the then Federation of British Industry informed the British Government that its members favoured the adoption of the metric system. The rationale behind the request was that 80% of British exports were to countries that used the metric system or that were considering changing to the metric system. The Board of Trade, on behalf of the Government, agreed to support a ten-year metrication programme. The government agreed to a voluntary policy requiring minimal legislation and costs to be borne where they fell. SI would be used from the outset.[73] The rest of the Commonwealth, South Africa and Ireland followed within a few years; in some countries such as South Africa and Australia metrication was mandatory rather than voluntary.[74][75]

text: By 1980 all apart from the United Kingdom, Canada and Ireland had effectively completed their programs. In the United Kingdom the breakdown of voluntary metrication in the mid-1970s[76]:§1.8 coincided with the United Kingdom's obligations as part of the EEC to adopt the metric system, resulting in legislation to force metrication in certain areas and the Eurosceptic movement adopting an anti-metrication stance and the United Kingdom seeking a number of derogations from the relevant EEC directives. Once the metrication of most consumer goods was completed in 2000, aspects of British life, especially in government, commerce and industry used SI.[76]:§1.6 & §1.10 Although imperial units are widely encountered in unregulated areas such as the press and everyday speech, SI or units approved for use alongside SI are used in most areas where units of measure are regulated. High-profile exceptions include the sale of draught beer, the sale of milk in returnable containers, and United Kingdom road signs. Irish road signs (road distances and speeds) were converted to metric units during the first decade of the 21st century;[77] otherwise, the situation in Ireland is similar to that in the United Kingdom.[78]

text: Canada has adopted it for most purposes, but imperial units are still legally permitted and remain in common use throughout a few sectors of Canadian society, particularly in the buildings, trades and railways sectors.[79][80]

text: European Union[edit]

text: In 1960, all the largest industrialised nations that had an established history of using the metric system were members of the European Economic Community (EEC).

text: In 1972, in order to harmonise units of measure as part of a programme to facilitate trade between member states, the EEC issued directive 71/354/EEC.[81] This directive catalogued units of measure that could be used for "economic, public health, public safety and administrative purposes" and also provided instructions for a transition from the existing units of measure that were in use. The directive replicated the CGPM SI recommendations and in addition pre-empted some of the additions whose use had been recommended by the CIPM in 1969, but had not been ratified by the CGPM.[Note 13] The directive also catalogued units of measure whose status would be reviewed by the end of 1977 (mainly coherent CGS units of measure) and also catalogued units of measure that were to be phased out by the end of 1977, including the use of obsolete names for the sale of timber such as the stere, the use of units of force and pressure that made use of the acceleration due to gravity,[Note 14] the use of non-coherent units of power such as the Pferdestärke (PS), the use of the calorie as a measure of energy and the stilb as a measure of luminance. The directive was silent in respect of units that were specific to one or two countries including the pond, pfund, livre (Dutch, German and French synonyms for 500 g), thereby effectively prohibiting their use as well.

text: When the directive was revisited during 1977, some of the older units that were being reviewed (such as millimetre of mercury for blood pressure)[Note 15] were retained but others were phased out, thereby broadly aligning the allowable units with SI. The directive was however overhauled to accommodate British and Irish interests in retaining the imperial system in certain circumstances.[82] It was reissued as directive 80/181/EEC. During subsequent revisions, the directive has reflected changes in the definition of SI. The directive also formalised the use of supplementary units, which in 1979 were permitted for a period of ten years. The cut-off date for the use of supplementary units was extended a number of times and in 2009 was extended indefinitely.[83]

text: India[edit]

text: India was one of the last countries to start a metrication programme before the advent of SI. When it became independent in 1947, both imperial and native units of measure were in use. Its metrication programme started in 1956 with the passing of the Standards of Weights and Measures Act. Part of the act fixed the value of the seer (a legacy unit of mass) to 0.9331 kg exactly; elsewhere the Act declared that from 1960 all non-metric units of measure were to be illegal.[85]

text: Four years after the Indian Government announced its metrication programme, SI was published. The result was that the initial metrication programme was a conversion to the CGS system of units and the subsequent adoption of SI has been haphazard. Originally the Indian Government had planned to replace all units of measure with metric units by 1960. In 1976 a new Weights and Measures Act replaced the 1956 Act which, amongst other things, required that all weighing devices be approved before being released onto the market place. However, in 2012, it was reported that traditional units were still encountered in small manufacturing establishments and in the marketplace alongside CGS, SI and imperial measures, particularly in the poorer areas.[86]

text: The use of the Indian numbering system of crores (7007100000000000000♠10000000) and lakhs (7005100000000000000♠100000), which do not map onto the SI system of prefixes, is widespread and is often found alongside or in place of the western numbering system.[87]

text: United States[edit]

text: Even though Congress set up a framework for the use of the metric system in the nineteenth century,[88][Note 16] the United States continues to use US customary units, based on English measure passed by parliament under the reign of Queen Anne in 1706, for most purposes apart from science and medicine.[89] In Puerto Rico, metric units are widely used due to its Spanish colonial history.[90]

text: On 10 February 1964, the National Bureau of Standards (now the National Institute of Standards and Technology) issued a statement that it was to use SI except where this would have an obvious detrimental effect. In 1968 Congress authorised the U.S. Metric Study, the emphasis of which was to examine the feasibility of adopting SI.[91] The first volume was delivered in 1970.[92] The study recommended that the United States adopt the International System of units,[93] and in 1975 Congress passed the Metric Conversion Act of 1975, which established a national policy of coordinating and planning for the increased use of the metric measurement system in the United States.[94] Metrication was voluntary and to be coordinated by the United States Metric Board (USMB).[95]

text: Efforts during the Ford and Carter administrations to force metrication were seized on by many newspaper editorialists as being dictatorial.[6]:365 Public response included resistance, apathy, and sometimes ridicule.[96] The underlying reasons for this response include a relative uniformity of weights and measures (though, notably, US liquid measure differed by about 20% from British Imperial measure, which was adopted throughout the British Empire in 1824) inherited from the United Kingdom in 1776, a homogeneous economy and the influence of business groups and populists in Congress caused the country to look at the short-term costs associated with the change-over, particularly those that would be borne by the consumer rather than long-term benefits of efficiency and international trade. The Metrication Board was disbanded under President Ronald Reagan's direction in 1982.[6]:362–365

text: The 1988 Omnibus Foreign Trade and Competitiveness Act removed international trade barriers and amended the Metric Conversion Act of 1975, designating the metric system as "the Preferred system of weights and measures for United States trade and commerce". The legislation stated that the federal government has a responsibility to assist industry, especially small business, as it voluntarily converts to the metric system of measurement.[97] Exceptions were made for the highway and construction industries; the Department of Transportation planned to require metric units by 2000, but this plan was cancelled by the 1998 highway bill TEA21.[98] However, the US military uses the metric system widely, partly because of the need to work with armed services from other nations.[99] Although overall responsibility for labelling requirements of consumer goods lies with Congress and is therefore covered by federal law, details of labelling requirements for certain commodities are controlled by state law or by other authorities such as the Food and Drug Administration, Environmental Protection Agency and Alcohol and Tobacco Tax and Trade Bureau.[100] The federal Fair Packaging and Labeling Act (FPLA), originally passed in 1964, was amended in 1992 to require consumer goods directly under its jurisdiction to be labelled in both customary and metric units. Some industries are engaged in efforts to amend this law to allow manufacturers to use only metric labelling.[101] The National Conference on Weights and Measures has developed the Uniform Packaging and Labeling Regulations (UPLR) which provides a standard approach to those sections of packaging law that are under state control. Acceptance of the UPLR varies from state to state – fourteen states accept it by merely citing it in their legislation.[102]

text: During the first decade of the 21st century, the EU directive 80/181/EEC had required that dual unit labelling of goods sold within the EU cease by the end of 2009. This was backed up by requests from other nations including Japan and New Zealand to permit metric-only labelling as an aid to trade with those countries.[100] Opinion in the United States was split – a bill to permit metric-only labelling at the federal level was to have been introduced in 2005 but significant opposition from the Food Marketing Institute, representing US grocers, has delayed the introduction of the bill. During a routine decennial review of the directive in 2008, the EU postponed the sunset clause for dual units indefinitely.

text: Meanwhile, in 1999 the UPLR was amended to permit metric-only labelling and automatically became law in those states that accept UPLR "as is". By 1 January 2009, 48 out of 50 states permit metric-only labelling, either through UPLR or through their own legislation.[100] As of February 2013[update] the use of metric (and therefore SI) units in the United States does not follow any pattern. Dual-unit labelling on consumer goods is mandatory. Some consumer goods such as soft drinks are sold in metric quantities, but milk is sold in customary units. The engineering industry is equally split. The automotive industry is largely metric,[103] but aircraft such as the Boeing 787 Dreamliner were designed using customary units.[104]

text: Redefinition of units[edit]

text: After the metre was redefined in 1960, the kilogram remained the only SI base unit that relied on a specific physical artefact, the international prototype of the kilogram (IPK), for its definition and thus the only unit that was still subject to periodic comparisons of national standard kilograms with the IPK.[105] After the 1996–1998 recalibration, a clear divergence between the various prototype kilograms was observed.[citation needed]

text: At its 23rd meeting, held in 2007, the CGPM recommended that the CIPM should continue to investigate methods to provide exact fixed values for physical constants of nature that could then be used in the definitions of units of measure in place of the IPK, thus enabling the transition from explicit unit definitions to explicit constant definitions.[106][107]

text: At a meeting of the CCU held in Reading, United Kingdom, in September 2010, a resolution and draft changes to the SI Brochure that were to be presented to the next meeting of the CIPM in October 2010 were agreed to in principle.[108][109] The proposals that the CCU put forward were:

text:
In addition to the speed of light, four constants of nature – the Planck constant, an elementary charge, the Boltzmann constant and the Avogadro number – be defined to have exact values.
The International prototype kilogram be retired
The current definitions of the kilogram, ampere, kelvin and mole be revised.
The wording of the definitions of all the base units be both tightened up and changed to reflect the change in emphasis from explicit unit to explicit constant definitions.

text: The CIPM meeting of October 2010 reviewed progress towards establishing fixed values for the constants but found that "the conditions set by the General Conference at its 23rd meeting have not yet been fully met. For this reason the CIPM does not propose a revision of the SI at the present time".[110]

text: At the 24th CGPM meeting, held in October 2011, the CIPM sponsored a resolution in which the requisite definition changes were agreed to in principle and in which the conditions required to be met before the redefinitions could be implemented were restated.[111]

text: By November 2014 the conditions set out at the 23rd meeting of the CGPM for the unit redefinitions had still not been met, and the 25th meeting of the CGPM, held in November 2014, adopted a similar resolution encouraging further work towards establishing fixed values for the fundamental constants.[112]

text: The redefinitions are expected to be adopted at the 26th CGPM in the fall of 2018.[113] The CODATA task group on fundamental constants has announced special submission deadlines for data to compute the values that will be announced at this event.[114]