1426:(it is actually extremely stable with a reproducibility of a few parts in 10). There would be no automatic effect on the metre because the second—and thus the metre's length—is abstracted via the laser comprising the metre's practical realisation. Scientists performing metre calibrations would simply continue to measure out the same number of laser wavelengths until an agreement was reached to do otherwise. The same is true with regard to the real-world dependency on the kilogram: if the mass of the IPK was found to have changed slightly, there would be no automatic effect upon the other units of measure because their practical realisations provide an insulating layer of abstraction. Any discrepancy would eventually have to be reconciled though, because the virtue of the SI system is its precise mathematical and logical harmony amongst its units. If the IPK's value were to have been definitively proven to have changed, one solution would have been to simply redefine the kilogram as being equal to the mass of the IPK plus an offset value, similarly to what had previously been done with its replicas; e.g., "the kilogram is equal to the mass of the
2734:
two other facts: that platinum has a strong affinity for mercury, and that atmospheric mercury is significantly more abundant in the atmosphere today than at the time the IPK and its replicas were manufactured. The burning of coal is a major contributor to atmospheric mercury and both
Denmark and Germany have high coal shares in electrical generation. Conversely, electrical generation in France, where the IPK is stored, is mostly nuclear. This theory is supported by the fact that the mass divergence rate—relative to the IPK—of Denmark's prototype, K48, since it took possession in 1949 is an especially high 78 μg per century while that of Germany's prototype has been even greater at
38:
739:
955:
559:. The latest verification performed in 1989 shows a mass precisely identical to its original 1889 value. Quite unlike transient variations such as this, the US's check standard, K4, has persistently declined in mass relative to the IPK—and for an identifiable reason: check standards are used much more often than primary standards and are prone to scratches and other wear. K4 was originally delivered with an official mass of
579:
2922:
2904:
2890:
2877:
2862:
2848:
2835:
305:
666:
the IPK, or an increase in that of its replicas dispersed throughout the world. Moreover, there are no technical means available to determine whether or not the entire worldwide ensemble of prototypes suffers from even greater long-term trends upwards or downwards because their mass "relative to an invariant of nature is unknown at a level below 1000
2738:
ever since it took possession of K55 in 1954. However, still other data for other replicas isn't supportive of this theory. This mercury absorption theory is just one of many advanced by the specialists to account for the relative change in mass. To date, each theory has either proven implausible, or
2733:
than the replicas. This theory begins with the observation that the IPK is uniquely stored under three nested bell jars whereas its six sister copies stored alongside it in the vault as well as the other replicas dispersed throughout the world are stored under only two. This theory is also founded on
542:
iridium (Pt‑10Ir) kilogram standards, two of which, K4 and K20, are from the original batch of 40 replicas distributed in 1884. The K20 prototype was designated as the primary national standard of mass for the US. Both of these, as well as those from other nations, are periodically returned to
2690:
Nos. 42′, 77 and 650 are called "standards" rather than "prototypes" because they are slightly underweight, slightly too much material having been removed when they were manufactured. Other than being more than 1 mg below the nominal 1 kg mass, they are identical to the prototypes, and are
1351:
Because the magnitude of many of the units composing the SI system of measurement was until 2019 defined by its mass, the quality of the IPK was diligently protected to preserve the integrity of the SI system. However, the average mass of the worldwide ensemble of prototypes and the mass of the IPK
2726:
rubbing with a chamois—if done carefully—did not alter the prototypes' mass. More recent cleaning experiments at the BIPM, which were conducted on one particular prototype (K63), and which benefited from the then-new NBS‑2 balance, demonstrated 2 μg stability. Experiments on prototypes
718:
that had been absorbed by the prototypes being in the proximity of mercury-based instruments. The IPK has been stored within centimetres of a mercury thermometer since at least as far back as the late 1980s. In this
Newcastle University work six platinum weights made in the nineteenth century were
665:
of mass over the last century, and possibly significantly more, in comparison to its official copies. The reason for this drift has eluded physicists who have dedicated their careers to the SI unit of mass. No plausible mechanism has been proposed to explain either a steady decrease in the mass of
533:
the kilogram. However, any changes in the IPK's mass over time could be deduced by comparing its mass to that of its official copies stored throughout the world, a rarely undertaken process called "periodic verification". The only three verifications occurred in 1889, 1948, and 1989. For instance,
660:
Because the first forty official copies are made of the same alloy as the IPK and are stored under similar conditions, periodic verification using a number of replicas—especially the national primary standards, which are rarely used—can convincingly demonstrate the stability of the IPK. What has
705:
It has been possible to rule out many explanations of the observed divergences in the masses of the world's prototypes proposed by scientists and the general public. The BIPM's FAQ explains, for example, that the divergence is dependent on the amount of time elapsed between measurements and not
1441:
The long-term solution to this problem, however, was to liberate the SI system from its dependency on the IPK by developing a practical realisation of the kilogram that can be reproduced in different laboratories by following a written specification. The units of measure in such a practical
657:μg per year thereafter. Since check standards like K4 are not cleaned for routine calibrations of other mass standards—a precaution to minimise the potential for wear and handling damage—the BIPM's model of time-dependent mass gain has been used as an "after cleaning" correction factor.
636:
days before verification. Before the BIPM's published report in 1994 detailing the relative change in mass of the prototypes, different standard bodies used different techniques to clean their prototypes. The NIST's practice before then was to soak and rinse its two prototypes first in
602:
Beyond the simple wear that check standards can experience, the mass of even the carefully stored national prototypes can drift relative to the IPK for a variety of reasons, some known and some unknown. Since the IPK and its replicas are stored in air (albeit under two or more nested
2779:
3. Data is for prototypes K1, K5, K6, K7, K8(41), K12, K16, K18, K20, K21, K24, K32, K34, K35, K36, K37, K38, and K40; and excludes K2, K23, and K39, which are treated as outliers. This is a larger data set than is shown in the chart at the top of this section, which corresponds to
2717:
Note that if the 50 μg difference between the IPK and its replicas was entirely due to wear, the IPK would have to have lost 150 million billion more platinum and iridium atoms over the last century than its replicas. That there would be this much wear, much less a
256:, below, for photographs). Three independently controlled keys are required to open the vault. Official copies of the IPK were made available to other nations to serve as their national standards. These were compared to the IPK roughly every 40 years, thereby providing
670:μg over a period of 100 or even 50 years". Given the lack of data identifying which of the world's kilogram prototypes has been most stable in absolute terms, it is equally valid to state that the first batch of replicas has, as a group, gained an average of about 25
2729: Many theories have been advanced to explain the divergence in the masses of the prototypes. One theory posits that the relative change in mass between the IPK and its replicas is not one of loss at all and is instead a simple matter that the IPK has
685:
over a period of about a month in its after-cleaned mass. The precise reason for this short-term instability is not understood but is thought to entail surface effects: microscopic differences between the prototypes' polished surfaces, possibly aggravated by
661:
become clear after the third periodic verification performed between 1988 and 1992 is that masses of the entire worldwide ensemble of prototypes have been slowly but inexorably diverging from each other. It is also clear that the IPK lost perhaps
284:, which continued to manufacture nearly all of the national prototypes as needed until the new definition of the kilogram came into effect in 2019. In 1883, the mass of the IPK was found to be indistinguishable from that of the
2945:
546:
Note that none of the replicas has a mass precisely equal to that of the IPK; their masses are calibrated and documented as offset values. For instance, K20, the US's primary standard, originally had an official mass of
649:μg more. After cleaning—even when they are stored under their bell jars—the IPK and its replicas immediately begin gaining mass again. The BIPM even developed a model of this gain and concluded that it averaged 1.11
2508:
Cumpson, Peter (October 2013). "Stability of reference masses: VI. Mercury and carbonaceous contamination on platinum weights manufactured at a similar time as the international and national prototype kilograms".
742:
Until May 2019, the magnitude of many of the units composing the SI system of measurement, including most of those used in the measurement of electricity and light, were highly dependent upon the stability of
611:
of atmospheric contamination onto their surfaces. Accordingly, they are cleaned in a process the BIPM developed between 1939 and 1946 known as "the BIPM cleaning method" that comprises firmly rubbing with a
1875:"Calibration campaign against the international prototype of the kilogram in anticipation of the redefinition of the kilogram part I: comparison of the international prototype with its official copies"
590:
measurements; no historical mass-measurement data is available to determine which of the prototypes has been most stable relative to an invariant of nature. There is the distinct possibility that
2046:Из 40 изготовленных копий прототипа две (№12 и №26) были переданы России. Эталон №12 принят в СССР в качестве государственного первичного эталона единицы массы, а №26 — в качестве эталона-копии.
586:, plus two of the IPK's sister copies: K32 and K8(41). All mass changes are relative to the IPK. The initial 1889 starting-value offsets relative to the IPK have been nulled. The above are all
543:
the BIPM for verification. Great care is exercised when transporting prototypes. In 1984, the K4 and K20 prototypes were hand-carried in the passenger section of separate commercial airliners.
2681:
Prototype No. 8(41) was accidentally stamped with the number 41, but its accessories carry the proper number 8. Since there is no prototype marked 8, this prototype is referred to as 8(41).
316:, which serve as primary standards for defining all units of mass and weight in the United States. This is a replica for public display, shown as it is normally stored, under two bell jars.
726:
The increasing divergence in the masses of the world's prototypes and the short-term instability in the IPK prompted research into improved methods to obtain a smooth surface finish using
2722:
of this magnitude, is thought unlikely; 50 μg is roughly the mass of a fingerprint. Specialists at the BIPM in 1946 carefully conducted cleaning experiments and concluded that even
2454:, which stated "The kilogram is in need of a new definition because the mass of the prototype is known to vary by several parts in 10 over periods of time of the order of a month ..." (
334:
Ten working copies: eight (9, 31, 42′, 63, 77, 88, 91, and 650) for routine use and two (25 and 73) for special use. Kept in the BIPM's calibration laboratory in Saint-Cloud, France.
832:(A), was defined as the current needed to produce a force of 0.2 μN between 2 parallel wires 1 m apart for every metre of length. Substituting these parameters into
706:
dependent on the number of times the prototype or its copies have been cleaned or possible changes in gravity or environment. Reports published in 2013 by Peter
Cumpson of
747:
The stability of the IPK was crucial because the kilogram underpinned much of the SI as defined and structured until 2019. The majority of SI units with special names are
2852:
714:
of samples that were stored alongside various prototype kilograms suggested that one source of the divergence between the various prototypes could be traced to
1486:
2979:
2958:
2264:
1360:
years ago. Further, the world's national metrology laboratories must wait for the fourth periodic verification to confirm whether the historical trends
2802:
Assuming the past trend continues, whereby the mean change in mass of the first batch of replicas relative to the IPK over one hundred years was +23.5
2908:
2867:
2971:
2926:
309:
2881:
1854:
1821:
1517:
1993:
242:(known by its French-language initials BIPM) in an environmentally monitored safe in the lower vault located in the basement of the BIPM's
239:
1994:"Director's Report on the Activity and Management of the International Bureau of Weights and Measures; Supplement: scientific Departments"
293:
1622:
959:
2572:
1725:
641:, then in ethanol, and to then clean them with a jet of bi-distilled water steam. Cleaning the prototypes removes between 5 and 60
1422:
wavelengths of light from this laser. Now suppose that the official measurement of the second was found to have drifted by a few
645:μg of contamination depending largely on the time elapsed since the last cleaning. Further, a second cleaning can remove up to 10
1093:, or were defined as the ratio of 2 quantities, both of which were related in the same way to the mass of the IPK, for example:
2839:
2072:
1605:
1459:
1193:
Here the newtons in the numerator and the denominator exactly cancel out when calculating the value of the ohm. Similarly:
771:, is defined in terms of the newton. This chain of dependency follows to many other SI units of measure. For instance, the
2894:
17:
2727:
No. 7 and 32 in
January 2014 showed less than 0.5 μg mass lost from a third complete cleaning and washing cycle.
2621:
1692:
881:
making the magnitude of the ampere proportional to the square root of the newton and hence of the mass of the IPK.
529:
Before 2019, by definition, the error in the measured value of the IPK's mass was exactly zero; the mass of the IPK
711:
94:. During that time, the IPK and its duplicates were used to calibrate all other kilogram mass standards on Earth.
2946:
Are any problems caused by having the kilogram defined in terms of a physical artefact? (FAQ - Mass & Density)
41:
The
International Prototype Kilogram, stored in a vault in Paris, was replaced in 2019 by a formula that uses the
763:. If the mass of the IPK were to change slightly then the newton would also change proportionally. In turn, the
3031:
1494:
1464:
280:), quickly leading to the production of the IPK. The IPK is one of three cylinders made in London in 1879 by
277:
76:, particularly by German-language authors writing in English) is an object whose mass was used to define the
2911:, the BIPM's modern precision balance featuring a standard deviation of one ten-billionth of a kilogram (0.1
2303:
2748:
The mean change in mass of the first batch of replicas relative to the IPK over one hundred years is +23.5
37:
1923:
G. Girard (1994). "The Third
Periodic Verification of National Prototypes of the Kilogram (1988–1992)".
1873:
Stock, Michael; Barat, Pauline; Davis, Richard S.; Picard, Alain; Milton, Martin J. T. (24 March 2015).
2095:
517:
98:
2665:, so it is often reported as being located there, but the grounds are in the commune of Saint-Cloud (
2450:
Report to the CGPM, 14th meeting of the
Consultative Committee for Units (CCU), April 2001, 2. (ii);
2116:
2032:
695:
928:
green light. Hence the magnitudes of the mole and candela were proportional to the mass of the IPK.
1078:
760:
2966:
2329:
2059:
1851:
1525:
833:
719:
all found to have mercury at the surface, the most contaminated of which had the equivalent of 250
2937:
kg maximum mass. Also used by NIST and Sandia
National Laboratories' Primary Standards Laboratory
2061:
13th
Comparison between the Swedish national kilogram and SP principal standards for one kilogram
1447:
153:
145:
110:
87:
82:
2700:
The other two Pt‑10Ir standards owned by the US are K79, from a new series of prototypes
2000:
730:
on newly manufactured replicas and was one of the reasons for the redefinition of the kilogram.
3021:
2263:
Mills, Ian M.; Mohr, Peter J; Quinn, Terry J; Taylor, Barry N; Williams, Edwin R (April 2005).
313:
653:μg per month for the first 3 months after cleaning and then decreased to an average of about 1
2241:
1808:
2518:
2344:
2279:
1966:
1932:
1888:
1637:
1566:
707:
243:
149:
31:
2604:
304:
8:
2666:
2486:
1653:
1442:
realisation would have their magnitudes precisely defined and expressed in terms of only
936:
885:
141:
2522:
2473:
2348:
2283:
1936:
1892:
1745:
1641:
1570:
3026:
2661:
The
Pavillon's (and hence the BIPM's) postal address is in the neighbouring commune of
2534:
2413:
2386:
2360:
2295:
2217:
2192:
2168:
2143:
1948:
897:
893:
681:
known specifically about the IPK is that it exhibits a short-term instability of about
320:
The IPK and its various copies are given the following designations in the literature:
120:
to reduce its surface area. The addition of 10% iridium improved upon the all-platinum
2538:
2530:
2418:
2364:
2356:
2299:
2291:
2222:
2173:
2068:
1979:
1952:
1944:
1901:
1874:
1601:
1550:
1443:
1429:
1423:
715:
594:
the prototypes gained mass over 100 years and that K21, K35, K40, and the IPK simply
331:
Six sister copies: K1, 7, 8(41), 32, 43 and 47. Stored in the same vault at the BIPM.
91:
2526:
2408:
2398:
2352:
2287:
2212:
2204:
2163:
2155:
1940:
1896:
1839:
From Artefacts to Atoms: The BIPM and the Search for Ultimate Measurement Standards
1737:
1645:
1574:
825:
269:
1649:
1858:
1595:
784:
748:
727:
629:
613:
281:
188:
42:
2897:, an Austrian-made precision balance, was used by the NIST from 1945 until 1960
2705:
2704:
that were diamond-turned directly to a finish mass, and K85, which is used for
1304:
738:
625:
506:
370:
220:
200:
67:
2739:
there are insufficient data or technical means to either prove or disprove it.
2455:
1741:
3015:
1794:
954:
801:
795:
764:
756:
617:
510:
273:
180:
160:
2595:, Journal of research of the National Institute of Standards and Technology
2025:
1780:
1487:"A brief history of the kilogram, and why scientists are ready to revise it"
2984:
2422:
2226:
2177:
2058:
Gutfelt, Bengt; Johansson, Mathias; Nyfeldt, Per; Pendrill, Leslie (2014).
1404:
typically takes the form of a helium–neon laser, and the metre's length is
1334:
1051:
1030:
969:
821:
474:
257:
224:
2980:"In the balance: scientists vote on first change to kilogram in a century"
1766:
892:, was defined prior to the revision as the number of atoms in 12 grams of
779:, is defined as that expended when a force of one newton acts through one
2629:
2403:
2208:
2197:
Journal of Research of the National Institute of Standards and Technology
2159:
2148:
Journal of Research of the National Institute of Standards and Technology
1700:
1446:. While major portions of the SI system are still based on the kilogram,
1282:
940:
889:
699:
520:
in Paris (34) and the Istituto di Metrologia G. Colonnetti in Turin (62).
490:
478:
434:
430:
325:
247:
204:
164:
578:
555:μg less than the IPK. A verification performed in 1948 showed a mass of
308:
National prototype kilogram K20, one of two prototypes stored at the US
2758:
The Third Periodic Verification of National Prototypes of the Kilogram
1879:
1852:
The international prototype of the kilogram and its six official copies
1097:
723:μg of mercury when scaled to the surface area of a kilogram prototype.
608:
516:
Some additional copies held by non-national organisations, such as the
418:
216:
117:
2452:
General Conference on Weights and Measures, 22nd Meeting, October 2003
1726:"New Techniques in the Manufacture of Platinum-Iridium Mass Standards"
1678:
1579:
1554:
976:
932:
921:
691:
466:
402:
366:
342:
338:
232:
196:
128:
while still retaining platinum's many virtues: extreme resistance to
54:
2662:
1390:
as the distance light travels in a vacuum during a time interval of
759:
is defined as the force necessary to accelerate one kilogram at one
768:
755:
offsetting relative to other, more basic, units. For instance, the
687:
604:
498:
470:
450:
442:
125:
102:
77:
3006:
1980:
Some BIPM calibrations and services in mass and related quantities
159:
By 2018, the IPK underpinned the definitions of four of the seven
987:
973:
901:
752:
638:
621:
454:
394:
390:
382:
374:
350:
346:
208:
172:
133:
106:
2563:
Davis, Journal of Research of the National Bureau of Standards,
1978:
The International Bureau of Weights and Measures official site:
1965:
The International Bureau of Weights and Measures official site:
1850:
The International Bureau of Weights and Measures official site:
1807:
The International Bureau of Weights and Measures official site:
1555:"An atomic physics perspective on the kilogram's new definition"
2951:
2067:. Borås: SP Technical Research Institute of Sweden. p. 3.
2057:
1369:
1090:
1082:
829:
776:
502:
494:
486:
462:
458:
446:
438:
426:
406:
386:
358:
354:
228:
168:
2265:"Redefinition of the kilogram: a decision whose time has come"
2868:
Steam cleaning a 1 kg prototype before a mass comparison
1822:"Standard Kilogram Weights: A Story of Precision Fabrication"
1383:
1197:
1086:
963:
947:
925:
807:
780:
772:
751:, meaning they are defined simply multiplying or dividing or
482:
422:
414:
410:
398:
378:
362:
212:
192:
129:
2243:
The washing and cleaning of kilogram prototypes at the BIPM
1999:. Bureau International des Poids et Mesures. Archived from
1545:
1543:
993:
813:
788:
288:
made eighty-four years prior, and was formally ratified as
184:
176:
137:
1077:
susceptible to changes in the mass of the IPK were either
981:
2141:
1540:
187:
respectively) as well as the definitions of every named
2391:
Journal of Research of the National Bureau of Standards
2387:"Recalibration of the U.S. National Prototype Kilogram"
698:
that slowly deposit onto the prototypes as well as the
2190:
2950:
International Bureau of Weights and Measures (BIPM):
2117:"Making the first international kilograms and metres"
1872:
563:
in 1889, but as of 1989 was officially calibrated at
272:
was signed on 20 May 1875 and further formalised the
97:
The IPK is a roughly golfball-sized object made of a
2262:
674:μg over one hundred years in comparison to the IPK.
238:
The IPK and its six sister copies are stored at the
27:
Physical artifact that formerly defined the kilogram
2553:
Recalibration of the US National Prototype Kilogram
1967:
Calibration and characterization certificates: Mass
1597:
Operational Symmetries: Basic Operations in Physics
1693:"(Former) International Prototype of the Kilogram"
1623:"High-accuracy mass spectrometry with stored ions"
958:A replica of the prototype kilogram on display at
733:
2193:"The Kilogram and Measurements of Mass and Force"
2144:"The Kilogram and Measurements of Mass and Force"
3013:
2882:The IPK and its six sister copies in their vault
551:(micrograms) in 1889; that is to say, K20 was 39
2855:resting on an egg crate fluorescent light panel
2581:The Kilogram and Measurements of Mass and Force
1549:
1378:of the SI units are quite different from their
2972:National Institute of Standards and Technology
324:The IPK itself, stored in the BIPM's vault in
310:National Institute of Standards and Technology
175:(whose definitions at the time referenced the
2944:The UK's National Physical Laboratory (NPL):
2434:
2432:
2184:
1450:on invariant, universal constants of nature.
966:, featuring the protective double glass bell.
113:with height equal to its diameter of about 39
45:, since the IPK’s mass is unstable over time.
1370:Insulating effects of practical realisations
632:, and allowing the prototypes to settle for
582:Mass drift over time of national prototypes
240:International Bureau of Weights and Measures
2384:
1518:"Missing Micrograms Set a Standard on Edge"
1356:μg since the third periodic verification 35
2429:
1587:
30:"IPK" redirects here. For other uses, see
2412:
2402:
2216:
2191:Z.J. Jabbour; S.L. Yaniv (Jan–Feb 2001).
2167:
1922:
1918:
1916:
1914:
1912:
1900:
1614:
1578:
1509:
1478:
2258:
2256:
1868:
1866:
1671:
953:
783:. Next to be affected is the SI unit of
737:
577:
303:
101:known as "Pt‑10Ir", which is 90%
86:, until 2019, when it was replaced by a
36:
2967:This Kilogram Has A Weight-Loss Problem
2853:K20, the US National Prototype Kilogram
2677:
2675:
2507:
2378:
2135:
1719:
1717:
1073:The SI derived units whose values were
931:These dependencies then extend to many
820:Furthermore, prior to the revision the
524:
260:of local measurements back to the IPK.
51:International Prototype of the Kilogram
14:
3014:
2977:
2441:, R. Steiner, NIST, Sep 11, 2007.
2239:
2096:"TÜBİTAK National Metrology Institute"
1991:
1909:
1593:
2909:The FB‑2 flexure-strip balance
2691:used during routine calibration work.
2327:
2253:
1863:
1723:
1620:
1515:
1484:
2684:
2672:
1714:
1460:Outline of metrology and measurement
702:-based solvents used to clean them.
571:Over a period of 110 years, K4 lost
299:
2142:Z. J. Jabbour; S. L. Yaniv (2001).
1679:"Resolution of the 1st CGPM (1889)"
960:Cité des Sciences et de l'Industrie
252:
140:and more than 21 times as dense as
24:
2752:μg with a standard deviation of 30
1841:. Oxford University Press. p. 321.
1400:of a second. However, the metre's
791:, which is one joule per second.
25:
3043:
2840:The IPK in three nested bell jars
2820:
2474:Getting the measure of a kilogram
1516:Lyall, Sarah (12 February 2011).
1448:the kilogram is now in turn based
109:(by mass) and is machined into a
2978:Sample, Ian (November 9, 2018).
2920:
2902:
2888:
2875:
2860:
2846:
2833:
2385:R. S. Davis (July–August 1985).
2328:Davis, Richard (December 2003).
1352:have likely diverged another 8.3
712:X-ray photoelectron spectroscopy
163:: the kilogram itself, plus the
80:from 1889, when it replaced the
2796:
2742:
2711:
2694:
2655:
2614:
2545:
2501:
2479:
2465:
2444:
2321:
2233:
2109:
2088:
2051:
2018:
1985:
1972:
1959:
1844:
1831:
1814:
1801:
1787:
1773:
1553:; Jamison, A. O. (1 May 2020).
734:Dependency of the SI on the IPK
337:National prototypes, stored in
250:on the outskirts of Paris (see
1759:
1685:
1485:Frost, Natasha (12 Nov 2018).
88:new definition of the kilogram
13:
1:
2959:What a kilogram really weighs
2439:Conjecture why the IPK drifts
1650:10.1016/j.physrep.2005.10.011
1471:
1465:International Prototype Metre
2121:National Physical Laboratory
1992:Picard, A. (February 2012).
1081:, derived entirely from the
7:
2626:Scientific work of the BIPM
2551:General section citations:
1857:September 26, 2007, at the
1621:Blaum, Klaus (March 2006).
1453:
263:
10:
3048:
2531:10.1088/0026-1394/50/5/518
2357:10.1088/0026-1394/40/6/001
2292:10.1088/0026-1394/42/2/001
1982:, retrieved August 4, 2013
1969:, retrieved August 4, 2013
1945:10.1088/0026-1394/31/4/007
1902:10.1088/0026-1394/52/2/310
1811:, retrieved August 4, 2013
696:volatile organic compounds
607:), they gain mass through
518:French Academy of Sciences
136:(almost twice as dense as
29:
3000:
2974:physicist Richard Steiner
2919:
2901:
2887:
2874:
2859:
2845:
2832:
2827:
2033:Great Soviet Encyclopedia
1742:10.1595/003214086X3027479
904:, was defined as that of
509:(18, 81 and 82), and the
3007:The BIPM YouTube channel
2648:
2026:
1079:dimensionless quantities
761:metre per second squared
567:and ten years later was
513:(20, 4, 79, 85 and 92).
286:Kilogramme des Archives
154:magnetic susceptibility
122:Kilogramme des Archives
111:right-circular cylinder
83:Kilogramme des Archives
65:; sometimes called the
2927:Mettler HK1000 balance
2893:NIST: This particular
2628:. BIPM. Archived from
1828:. 17 (2) (1973) 66-68
1730:Platinum Metals Review
1380:practical realisations
967:
816:= J/s = N m/s = kg m/s
744:
616:soaked in equal parts
599:
317:
314:Gaithersburg, Maryland
276:(a predecessor to the
150:thermal conductivities
124:by greatly increasing
99:platinum–iridium alloy
46:
3032:Standards (metrology)
2933:μg resolution and a 4
2330:"The SI unit of mass"
1724:Quinn, T. J. (1986).
1428:IPK + 42
1402:practical realisation
957:
896:and the base unit of
741:
581:
575:relative to the IPK.
307:
40:
2970:, an interview with
2404:10.6028/jres.090.015
2309:on November 20, 2011
2209:10.6028/jres.106.003
2160:10.6028/jres.106.003
2030:[Kilogram].
2006:on December 31, 2013
1382:. For instance, the
708:Newcastle University
525:Stability of the IPK
292:kilogram by the 1st
244:Pavillon de Breteuil
32:IPK (disambiguation)
2767:Girard, Metrologia
2523:2013Metro..50..518C
2349:2003Metro..40..299D
2284:2005Metro..42...71M
2240:Girard, G. (1990),
1937:1994Metro..31..317G
1893:2015Metro..52..310S
1826:Platinum Metals Rev
1642:2006PhR...425....1B
1594:Saller, H. (2017).
1571:2020PhT....73e..32K
886:amount of substance
1528:on 21 October 2017
1522:The New York Times
1444:physical constants
968:
898:luminous intensity
834:Ampère's force law
745:
690:absorption due to
600:
365:(60 and 64; 75 in
318:
300:Copies of the IPK
92:physical constants
90:based entirely on
47:
18:Prototype kilogram
2941:
2940:
2895:Rueprecht Balance
2460:MB ZIP file, here
2074:978-91-87461-72-9
1607:978-3-319-58664-9
1580:10.1063/PT.3.4472
1434:(equivalent to 42
1430:parts per billion
1424:parts per billion
884:The base unit of
775:, the SI unit of
767:, the SI unit of
534:the US owns five
481:(39, 72 and 84),
429:(21, 90 and 96),
417:(6, 94 and E59),
393:(52, 55 and 70),
132:, extremely high
16:(Redirected from
3039:
2996:
2994:
2992:
2936:
2932:
2924:
2923:
2914:
2906:
2905:
2892:
2891:
2879:
2878:
2864:
2863:
2850:
2849:
2837:
2836:
2825:
2824:
2814:
2813:
2811:
2805:
2800:
2794:
2792:
2787:
2783:
2778:
2774:
2766:
2761:
2755:
2751:
2746:
2740:
2737:
2715:
2709:
2703:
2698:
2692:
2688:
2682:
2679:
2670:
2659:
2642:
2641:
2639:
2637:
2618:
2612:
2608:
2602:
2590:
2586:
2576:
2570:
2562:
2558:
2549:
2543:
2542:
2505:
2499:
2498:
2496:
2494:
2483:
2477:
2469:
2463:
2459:
2448:
2442:
2436:
2427:
2426:
2416:
2406:
2382:
2376:
2375:
2373:
2371:
2334:
2325:
2319:
2318:
2316:
2314:
2308:
2302:. Archived from
2269:
2260:
2251:
2250:
2248:
2237:
2231:
2230:
2220:
2188:
2182:
2181:
2171:
2139:
2133:
2132:
2130:
2128:
2113:
2107:
2106:
2104:
2102:
2092:
2086:
2085:
2083:
2081:
2066:
2055:
2049:
2048:
2043:
2041:
2022:
2016:
2015:
2013:
2011:
2005:
1998:
1989:
1983:
1976:
1970:
1963:
1957:
1956:
1920:
1907:
1906:
1904:
1870:
1861:
1848:
1842:
1835:
1829:
1818:
1812:
1805:
1799:
1798:
1795:"Candela – BIPM"
1791:
1785:
1784:
1777:
1771:
1770:
1763:
1757:
1756:
1754:
1753:
1744:. Archived from
1721:
1712:
1711:
1709:
1708:
1699:. Archived from
1689:
1683:
1682:
1675:
1669:
1668:
1666:
1664:
1658:
1652:. Archived from
1627:
1618:
1612:
1611:
1591:
1585:
1584:
1582:
1547:
1538:
1537:
1535:
1533:
1524:. Archived from
1513:
1507:
1506:
1504:
1502:
1493:. Archived from
1482:
1437:
1433:
1421:
1420:
1416:
1413:
1408:—not defined—as
1399:
1398:
1394:
1364:
1359:
1355:
1340:
1331:
1329:
1328:
1319:
1316:
1314:
1300:
1298:
1297:
1294:
1291:
1279:
1277:
1276:
1267:
1264:
1262:
1254:
1252:
1251:
1241:
1238:
1231:
1229:
1228:
1225:
1222:
1215:
1213:
1212:
1209:
1206:
1182:
1178:
1176:
1175:
1167:
1163:
1160:
1153:
1151:
1150:
1141:
1138:
1131:
1129:
1128:
1125:
1122:
1115:
1113:
1112:
1109:
1106:
1069:
1067:
1066:
1063:
1060:
1048:
1046:
1045:
1042:
1039:
1027:
1025:
1024:
1021:
1018:
1011:
1009:
1008:
1005:
1002:
984:= lm/m = cd sr/m
919:
917:
916:
913:
910:
876:
874:
873:
864:
861:
826:electric current
804:= N/m = kg/(m s)
722:
684:
673:
669:
664:
656:
652:
648:
644:
635:
598:than the others.
585:
574:
570:
566:
562:
558:
554:
550:
541:
537:
270:Metre Convention
144:), satisfactory
116:
53:(referred to by
21:
3047:
3046:
3042:
3041:
3040:
3038:
3037:
3036:
3012:
3011:
3003:
2990:
2988:
2934:
2930:
2921:
2912:
2903:
2889:
2876:
2861:
2847:
2834:
2828:External images
2823:
2818:
2817:
2809:
2807:
2803:
2801:
2797:
2793:
2790:
2788:Girard's paper.
2785:
2781:
2776:
2772:
2764:
2759:
2753:
2749:
2747:
2743:
2735:
2728:
2716:
2712:
2701:
2699:
2695:
2689:
2685:
2680:
2673:
2660:
2656:
2651:
2646:
2645:
2635:
2633:
2632:on May 14, 2011
2620:
2619:
2615:
2606:
2600:
2588:
2584:
2574:
2568:
2560:
2556:
2550:
2546:
2506:
2502:
2492:
2490:
2485:
2484:
2480:
2470:
2466:
2457:
2449:
2445:
2437:
2430:
2383:
2379:
2369:
2367:
2332:
2326:
2322:
2312:
2310:
2306:
2267:
2261:
2254:
2246:
2238:
2234:
2189:
2185:
2140:
2136:
2126:
2124:
2115:
2114:
2110:
2100:
2098:
2094:
2093:
2089:
2079:
2077:
2075:
2064:
2056:
2052:
2039:
2037:
2028:
2024:
2023:
2019:
2009:
2007:
2003:
1996:
1990:
1986:
1977:
1973:
1964:
1960:
1921:
1910:
1871:
1864:
1859:Wayback Machine
1849:
1845:
1836:
1832:
1819:
1815:
1806:
1802:
1793:
1792:
1788:
1781:"Ampere - BIPM"
1779:
1778:
1774:
1765:
1764:
1760:
1751:
1749:
1722:
1715:
1706:
1704:
1691:
1690:
1686:
1677:
1676:
1672:
1662:
1660:
1659:on 4 April 2018
1656:
1630:Physics Reports
1625:
1619:
1615:
1608:
1592:
1588:
1548:
1541:
1531:
1529:
1514:
1510:
1500:
1498:
1483:
1479:
1474:
1456:
1435:
1427:
1418:
1414:
1411:
1409:
1396:
1392:
1391:
1372:
1365:
1362:
1357:
1353:
1346:
1338:
1326:
1320:
1317:
1312:
1311:
1310:
1308:
1295:
1292:
1289:
1288:
1286:
1274:
1268:
1265:
1260:
1259:
1258:
1256:
1249:
1242:
1239:
1236:
1235:
1233:
1226:
1223:
1220:
1219:
1217:
1210:
1207:
1204:
1203:
1201:
1188:
1180:
1174:
1165:
1164:
1161:
1158:
1157:
1155:
1149:
1142:
1139:
1136:
1135:
1133:
1126:
1123:
1120:
1119:
1117:
1110:
1107:
1104:
1103:
1101:
1064:
1061:
1058:
1057:
1055:
1043:
1040:
1037:
1036:
1034:
1022:
1019:
1016:
1015:
1013:
1006:
1003:
1000:
999:
997:
914:
911:
908:
907:
905:
872:
865:
862:
859:
858:
856:
846:
736:
728:diamond turning
720:
682:
671:
667:
662:
654:
650:
646:
642:
633:
630:distilled water
583:
572:
568:
564:
560:
556:
552:
548:
539:
535:
527:
302:
282:Johnson Matthey
266:
253:External images
189:SI derived unit
114:
43:Planck constant
35:
28:
23:
22:
15:
12:
11:
5:
3045:
3035:
3034:
3029:
3024:
3010:
3009:
3002:
2999:
2998:
2997:
2975:
2962:
2954:
2948:
2939:
2938:
2917:
2916:
2899:
2898:
2885:
2884:
2872:
2871:
2857:
2856:
2843:
2842:
2830:
2829:
2822:
2821:External links
2819:
2816:
2815:
2795:
2789:
2741:
2736:126 μg/century
2710:
2706:Kibble balance
2693:
2683:
2671:
2653:
2652:
2650:
2647:
2644:
2643:
2613:
2567:(4): 263-281,
2544:
2517:(5): 518–531.
2500:
2478:
2464:
2443:
2428:
2397:(4): 263–283.
2377:
2343:(6): 299–305.
2320:
2252:
2232:
2183:
2134:
2108:
2087:
2073:
2050:
2017:
1984:
1971:
1958:
1931:(4): 317–336.
1908:
1887:(2): 310–316.
1862:
1843:
1830:
1813:
1800:
1786:
1772:
1758:
1713:
1684:
1670:
1613:
1606:
1586:
1539:
1508:
1497:on 9 June 2020
1476:
1475:
1473:
1470:
1469:
1468:
1462:
1455:
1452:
1371:
1368:
1361:
1349:
1348:
1344:
1332:
1324:
1302:
1280:
1272:
1247:
1191:
1190:
1186:
1172:
1147:
1071:
1070:
1049:
1033:= V s = J/A =
1028:
996:= W/A = J/C =
991:
985:
979:
951:
879:
878:
870:
849:
848:
847:A/m = 0.2 μN/m
844:
818:
817:
811:
810:= N m = kg m/s
805:
799:
735:
732:
626:steam cleaning
624:, followed by
569:1 kg − 116 μg.
536:90% platinum /
526:
523:
522:
521:
514:
507:United Kingdom
371:Czech Republic
335:
332:
329:
301:
298:
265:
262:
201:degree Celsius
26:
9:
6:
4:
3:
2:
3044:
3033:
3030:
3028:
3025:
3023:
3022:Units of mass
3020:
3019:
3017:
3008:
3005:
3004:
2987:
2986:
2981:
2976:
2973:
2969:
2968:
2963:
2961:
2960:
2955:
2953:
2949:
2947:
2943:
2942:
2929:, featuring 1
2928:
2918:
2910:
2900:
2896:
2886:
2883:
2873:
2870:
2869:
2858:
2854:
2844:
2841:
2831:
2826:
2799:
2770:
2762:
2745:
2732:
2725:
2721:
2714:
2707:
2697:
2687:
2678:
2676:
2668:
2667:OpenStreetMap
2664:
2658:
2654:
2631:
2627:
2623:
2617:
2610:
2598:
2594:
2582:
2578:
2566:
2554:
2548:
2540:
2536:
2532:
2528:
2524:
2520:
2516:
2512:
2504:
2488:
2482:
2476:
2475:
2468:
2461:
2453:
2447:
2440:
2435:
2433:
2424:
2420:
2415:
2410:
2405:
2400:
2396:
2392:
2388:
2381:
2366:
2362:
2358:
2354:
2350:
2346:
2342:
2338:
2331:
2324:
2305:
2301:
2297:
2293:
2289:
2285:
2281:
2277:
2273:
2266:
2259:
2257:
2245:
2244:
2236:
2228:
2224:
2219:
2214:
2210:
2206:
2202:
2198:
2194:
2187:
2179:
2175:
2170:
2165:
2161:
2157:
2153:
2149:
2145:
2138:
2122:
2118:
2112:
2097:
2091:
2076:
2070:
2063:
2062:
2054:
2047:
2035:
2034:
2029:
2021:
2002:
1995:
1988:
1981:
1975:
1968:
1962:
1954:
1950:
1946:
1942:
1938:
1934:
1930:
1926:
1919:
1917:
1915:
1913:
1903:
1898:
1894:
1890:
1886:
1882:
1881:
1876:
1869:
1867:
1860:
1856:
1853:
1847:
1840:
1837:Terry Quinn.
1834:
1827:
1823:
1817:
1810:
1809:Verifications
1804:
1796:
1790:
1782:
1776:
1768:
1767:"Mole - BIPM"
1762:
1748:on 2015-09-24
1747:
1743:
1739:
1735:
1731:
1727:
1720:
1718:
1703:on 2020-03-12
1702:
1698:
1694:
1688:
1680:
1674:
1655:
1651:
1647:
1643:
1639:
1635:
1631:
1624:
1617:
1609:
1603:
1599:
1598:
1590:
1581:
1576:
1572:
1568:
1564:
1560:
1559:Physics Today
1556:
1552:
1546:
1544:
1527:
1523:
1519:
1512:
1496:
1492:
1488:
1481:
1477:
1466:
1463:
1461:
1458:
1457:
1451:
1449:
1445:
1439:
1431:
1425:
1407:
1403:
1389:
1385:
1381:
1377:
1374:Fortunately,
1367:
1343:
1336:
1333:
1323:
1306:
1303:
1284:
1281:
1271:
1246:
1199:
1196:
1195:
1194:
1185:
1171:
1146:
1099:
1096:
1095:
1094:
1092:
1088:
1084:
1080:
1076:
1053:
1050:
1032:
1029:
995:
992:
989:
986:
983:
980:
978:
975:
971:
965:
961:
956:
952:
949:
946:
945:
944:
942:
938:
934:
929:
927:
923:
903:
899:
895:
891:
887:
882:
869:
854:
853:
852:
843:
839:
838:
837:
835:
831:
827:
823:
815:
812:
809:
806:
803:
800:
797:
794:
793:
792:
790:
786:
782:
778:
774:
770:
766:
762:
758:
754:
750:
749:derived units
740:
731:
729:
724:
717:
713:
710:based on the
709:
703:
701:
697:
693:
689:
680:
675:
658:
640:
631:
627:
623:
619:
615:
610:
606:
597:
593:
589:
580:
576:
565:1 kg − 106 μg
544:
532:
519:
515:
512:
511:United States
508:
504:
500:
496:
493:(38 and 89),
492:
489:(40 and 86),
488:
484:
480:
476:
473:(41 and 65),
472:
468:
465:(11 and 29),
464:
461:(12 and 26),
460:
456:
452:
448:
444:
440:
436:
432:
428:
424:
420:
416:
412:
408:
404:
400:
396:
392:
388:
384:
380:
376:
372:
368:
364:
361:(50 and 74),
360:
356:
353:(28 and 37),
352:
348:
345:(44 and 87),
344:
340:
336:
333:
330:
327:
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2304:the original
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1729:
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1701:the original
1697:www.bipm.org
1696:
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1673:
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1654:the original
1633:
1629:
1616:
1600:. Springer.
1596:
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1526:the original
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557:1 kg − 19 μg
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475:South Africa
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937:photometric
753:in one case
700:hydrocarbon
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479:South Korea
435:North Korea
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2720:difference
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2337:Metrologia
2272:Metrologia
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1707:2019-05-29
1472:References
1406:delineated
941:electrical
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663:50 μg
609:adsorption
573:41 μg
419:Kazakhstan
152:, and low
146:electrical
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3027:Metrology
2952:Home page
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2027:Килограмм
2010:August 3,
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1285:= J/kg =
1054:= Wb/m =
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894:carbon 12
692:catalysis
605:bell jars
467:Singapore
403:Indonesia
367:Hong Kong
343:Australia
339:Argentina
328:, France.
296:in 1889.
233:steradian
197:becquerel
130:oxidation
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2101:June 16,
1855:Archived
1454:See also
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1307:= 1/Ω =
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1100:= V/A =
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798:= kg m/s
769:pressure
688:hydrogen
628:with bi-
588:relative
499:Thailand
471:Slovakia
451:Portugal
443:Pakistan
264:Creation
126:hardness
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103:platinum
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2579:); and
2519:Bibcode
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395:Hungary
391:Germany
383:Finland
375:Denmark
351:Belgium
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