Editing Yard (section)

===Definition of the yard in terms of the meter===
Subsequent measurements revealed that the yard standard and its copies were shrinking at the rate of one part per million every twenty years due to the gradual release of strain incurred during the fabrication process.<ref>{{cite web
|title = History of Calibration
|url = http://www.nisltd.co.uk/asp/default.aspx?page=history_of_calibration
|publisher = Norwich Instrument Services
|year = 2012}}</ref><ref>{{cite web
|title = The Gauge Block Handbook
|url = http://emtoolbox.nist.gov/Publications/NISTMonograph180.pdf
|publisher = The National Institute of Standards and Technology (NIST)
|year = 2013}}</ref>
The [[international prototype meter]], on the other hand, was comparatively stable. A measurement made in 1895 determined the length of the meter at {{val|39.370113}} inches relative to the imperial standard yard. The [[Weights and Measures (Metric System) Act 1897]]<ref name="The Law journal reports">{{cite book |editor-first=John |editor-last=Mews |title=The Law journal reports|chapter-url=https://books.google.com/books?id=4icyAAAAIAAJ&pg=RA2-PA109|volume=66|year=1897|publisher=The Law Journal Reports|location=London|page=109|chapter=Statutes of the Realm – 60–61 Victoria}}</ref> ([[60 & 61 Vict.]] c. 46) in conjunction with Order in Council 411 (1898) made this relationship official. After 1898, the ''de facto'' legal definition of the yard came to be accepted as {{frac|36|{{val|39.370113}}}} of a meter.

The yard (known as the "international yard" in the United States) was legally defined to be exactly 0.9144 [[meter]] in 1959 under an agreement in 1959 between Australia, Canada, New Zealand, South Africa, the United Kingdom and the United States.<ref name="Astin">A. V. Astin & H. Arnold Karo, (1959), [http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf ''Refinement of values for the yard and the pound''], Washington DC: [[National Bureau of Standards]], republished on [[National Geodetic Survey]] web site and the [[Federal Register]] (Doc. 59-5442, Filed, June 30, 1959, 8:45 a.m.)</ref> In the UK, the provisions of the treaty were ratified by the [[Weights and Measures Act 1963]]. The Imperial Standard Yard of 1855 was renamed the United Kingdom Primary Standard Yard and retained its official status as the national prototype yard.<ref name="Zupko1990-1963">{{cite book|author=Ronald Edward Zupko|author-link=Ronald Edward Zupko|title=Revolution in measurement: Western European weights and measures since the age of science|url=https://archive.org/details/bub_gb_uYCNFkRgXCoC|year=1990|publisher=American Philosophical Society|isbn=978-0-87169-186-6|page=[https://archive.org/details/bub_gb_uYCNFkRgXCoC/page/n444 432]}}</ref><ref>[http://www.legislation.gov.uk/ukpga/1985/72/schedule/2 Weights and Measures Act 1985 Baily's Metal. Parliamentary Copy (VI) of the Imperial Standard Yard. 41 & 42 Victoria, Chapter 49. Standard Yard at 62° Faht. Cast in 1878]</ref>