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s of a barleycorn is the inch".[12]

King David I of Scotland in his Assize of Weights and Measures (c. 1150) is said to have defined the Scottish inch as the width of an average man's thumb at the base of the nail, even including the requirement to calculate the average of a small, a medium, and a large man's measures.[13] However, the oldest surviving manuscripts date from the early 14th century and appear to have been altered with the inclusion of newer material.[14]

Charles Butler, a mathematics teacher at Penny Cyclopædia, observing that standard measures had since surpassed the barleycorn definition of the inch, and that to recover the inch measure from its original definition, in the event that the standard measure were destroyed, would involve the measurement of large numbers of barleycorns and taking their average lengths. He noted that this process would not perfectly recover the standard, since it might introduce errors of anywhere between one hundredth and one tenth of an inch in the definition of a yard.[17]

Scottish inch

The now obsolete Scottish inch (Scottish Gaelic: òirleach), 1/12 of a Scottish foot, was about 1.0016 imperial inches (about 2.5441 cm).[18] It was used in the popular expression Gie 'im an inch, an he'll tak an ell, in English "Give him an inch and he'll take an ell", first published as "For when I gave you an inch, you tooke an ell" by John Heywood in 1546.[19] (The ell, equal to 37 inches (about 94 cm), was in use in England until 1685.)[20]

Continental inches

Before the adoption of the metric system, several European countries had customary units whose name translates into "inch". The French pouce measured 2.70 cm, at least when applied to describe the calibre of artillery pieces (see also: Units of measurement in France). The Amsterdam foot (voet) consisted of 11 Amsterdam inches (duim) (see Dutch units of measurement). The Amsterdam foot is about 8% shorter than an English foot.

Modern standardisation

The current internationally accepted value for the imperial and US customary inch is exactly 25.4 millimetres.[21] This is based on the international yard of exactly 0.9144 metres adopted through the International yard and pound agreement in 1959.[22] Before the adoption of the international inch various definitions were in use. In the United Kingdom and most countries of the British Commonwealth the inch was defined in terms of the Imperial Standard Yard. The United States adopted the conversion factor 1 metre = 39.37 inches by an act in 1866,[1] and in 1893 Mendenhall ordered the physical realization of the inch be based on the international prototype metres numbers 21 and 27, which had been received from the CGPM together with the previously adopted conversion factor.[23]

In 1930 the British Standards Institution adopted an inch of exactly 25.4 mm. The American Standards Association followed suit in 1933. By 1935 industry in 16 countries had adopted the "industrial inch" as it came to be known.[24][25]

In 1946 the Commonwealth Science Congress recommended a yard of exactly 0.9144 metres for adoption throughout the British Commonwealth. This was adopted by Canada in 1951.[26] The United States, the United Kingdom, Canada, Australia, New Zealand and South Africa signed a treaty agreeing to the same standards on 1 July 1959.[27] This gives an inch of exactly 25.4 mm. However, the United States retains the 1/39.37-metre definition for survey purposes creating a slight difference between the international and US survey inches; the difference is exactly 2 millionths of the US survey inch.[28] This is approximately 1/8-inch in a mile.

See also


  1. ^ Corpus of Contemporary American English (Brigham Young University. Retrieved December 2011) lists 24,302 instances of inch(es) compared to 1548 instances of centimeter(s) and 1343 instances of millimeter(s).
  2. ^ Weights and Measures Act
  3. ^ Weights and Measures Act. Retrieved January 2012, Act current to 18 January 2012. Canadian units (5) The Canadian units of measurement are as set out and defined in Schedule II, and the symbols and abbreviations therefore are as added pursuant to subparagraph 6(1)(b)(ii).
  4. ^ a b Guidance Note on the use of Metric Units of Measurement by the Public Sector. Department for Business Innovation and Skills. Crown copyright 2011. Retrieved December 2011.
  5. ^ "The Traffic Signs Regulations and General Directions 2002 - No. 3113 - Schedule 2 - Regulatory Signs". UK: The National Archives. 2002. Retrieved 2013-04-25. 
  6. ^ "Climate Data Online – definition of rainfall statistics".  
  7. ^ Goetz, Hans-Werner; Jarnut, Jörg;  
  8. ^ Wilkins, David (1871). Councils and Ecclesiastical Documents Relating to Great Britain and Ireland: English church during the Anglo-Saxon period: A.D. 595-1066. 1871. Clarendon Press. p. 48. Retrieved 27 November 2011. 
  9. ^  
  10. ^ a b H. Arthur Klein (1974). The world of measurements: masterpieces, mysteries and muddles of metrology. New York: Simon and Schuster. 
  11. ^ Jane Hawkes and Susan Mills (1999). Northumbria's Golden Age. Sutton. p. 310.  
  12. ^ John Williams (1867). "The civil arts — mensuration". The Traditionary Annals of the Cymry. Tenby: R. Mason. pp. 243–245. 
  13. ^  
  14. ^ Elizabeth Gemmill; Nicholas Mayhew (22 June 2006). Changing Values in Medieval Scotland: A Study of Prices, Money, and Weights and Measures. Cambridge University Press. p. 113.  
  15. ^ a b Charles Butler (1814). An Easy Introduction to the Mathematics. Oxford: Bartlett and Newman. p. 61. 
  16. ^ John Bouvier (1843). "Barleycorn". A Law Dictionary: With References to the Civil and Other Systems of Foreign Law. Philadelphia: T. & J. W. Johnson. p. 188. 
  17. ^ George Long (1842). "Weights & Measures, Standard". The Penny Cyclopædia of the Society for the Diffusion of Useful Knowledge. London: Charles Knight & Co. p. 436. 
  18. ^ "Dictionary of the Scots Language". Edinburgh: Scottish Language Dictionaries. Retrieved 21 May 2011. 
  19. ^ Heywood, John (1546). A dialogue conteinying the nomber in effect of all the prouerbes in the englishe tongue, compacte in a matter concernyng two maner of mariages, etc. London: Thomas Berthelet.  Full text of 1874 reprint
  20. ^ Gibson, A. J. S.;  
  21. ^ "On what basis is one inch exactly equal to 25.4 mm? Has the imperial inch been adjusted to give this exact fit and if so when?". National Physical Laboratory. 25 March 2010. Retrieved 5 April 2013. 
  22. ^ Astin, A.V.; Karo, H. A.; Mueller, F.H. (25 June 1959). "Refinement of Values for the Yard and the Pound". US  
  23. ^  
  24. ^ National Conference on Weights and Measures; United States. Bureau of Standards;  
  25. ^ Wandmacher, Cornelius; Johnson, Arnold Ivan (1995). Metric Units in Engineering--going SI: How to Use the International Systems of Measurement Units (SI) to Solve Standard Engineering Problems. ASCE Publications. p. 265.  
  26. ^ National Conference on Weights and Measures; United States. Bureau of Standards;  
  27. ^  
  28. ^ A. V. Astin & H. Arnold Karo, (1959), 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 am)
  • Collins Encyclopedia of Scotland
  • Weights and Measures, by D. Richard Torrance, SAFHS, Edinburgh, 1996, ISBN 1-874722-09-9 (NB book focusses on Scottish weights and measures exclusively)
  • This article incorporates text from "Dwelly's [Scottish] Gaelic Dictionary" (1911).
  • Scottish National Dictionary and Dictionary of the Older Scottish Tongue
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