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For other uses, see Yard (disambiguation).
1 yard =
Imperial & US customary units
36 in 3 ft
SI units
0.9144 m
The informal public imperial measurement standards erected at the Royal Observatory, Greenwich, London, in the 19th century: 1 British yard, 2 feet, 1 foot, 6 inches, and 3 inches. The inexact monument was designed to permit rods of the correct measure to fit snugly into its pins at an ambient temperature of 62 °F (162⁄3 °C).[1][2]
Bronze Yard №11, the official standard of length for the United States between 1855 and 1892, when the Treasury Department formally adopted a metric standard. Bronze Yard №11 was forged to be an exact copy of the British Imperial Standard Yard held by Parliament. Both are line standards: the yard was defined by the distance at 62°F between two fine lines drawn on gold plugs (closeup, top) installed in recesses near each end of the bar.
Two yardsticks, used for measuring "yard goods"

The yard (abbreviation: yd) is an English unit of length, in both the British imperial and US customary systems of measurement, that comprises 3 feet or 36 inches. It is by international agreement in 1959 standardized as exactly 0.9144 meters. A metal yardstick originally formed the physical standard from which all other units of length were officially derived in both English systems.

In the 19th and 20th centuries, increasingly powerful microscopes and scientific measurement detected variation in these prototype yards which became significant as technology improved. In 1959, the United States, United Kingdom, Australia, New Zealand, and South Africa agreed to adopt the Canadian compromise value of 0.9144 meters per yard.

The term yard is also sometimes used for translating related lengths in other systems.

Name

See also: yardland, ell, and rod.

The name derives from the Old English gerd, gyrd, &c., which was used for branches, staves, and measuring rods.[3] It is first attested in the late-7th century laws of Ine of Wessex,[4] where the "yard of land" mentioned[4] is the yardland, an old English unit of tax assessment equal to 1⁄4 hide.[n 1] Around the same time, the Lindisfarne Gospel's account of the messengers from John the Baptist in the Book of Matthew[5] used it for a branch swayed by the wind.[3] In addition to the yardland, Old and Middle English both used their forms of "yard" to denote the surveying lengths of 15 or 16+1⁄2 ft used in computing acres, a distance now usually known as the "rod".[3]

A unit of three English feet is attested in a statute of c. 1300 (see below) but there it is called an ell (Template:Lang-la, lit. "arm"), a separate and usually longer unit of around 45 inches. The use of the word "yard" (Template:Lang-enm or ȝerde) to describe this length is first attested in Langland's poem on Piers Plowman.[3][n 2] The usage seems to derive from the prototype standard rods held by the king and his magistrates (see below).

The word "yard" is a homonym of "yard" in the sense of an enclosed area of land. This second meaning of "yard" has an etymology related to the verb "to gird" and is probably not related.[8][9]

History

Origin

The origin of the measure is uncertain. Both the Romans and the Welsh used multiples of a shorter foot, but 2+1⁄2 Roman feet was a "step" (gradus) and 3 Welsh feet was a "pace" (cam). The Proto-Germanic cubit or arm's-length has been reconstructed as *alinâ, which developed into the Old English ęln, Middle English elne, and modern ell of 1¼ yd. This has led some to derive the yard of three English feet from pacing; others from the ell or cubit; others from Henry I's arm standard (see below). Based on the etymology of the other "yard", others suggest it originally derived from the girth of a person's waist, while others believe it originated as a cubic measure.

The earliest record of a prototype measure is the statute II Edgar Cap. 8 (AD 959 x 963), which survives in several variant manuscripts. In it, Edgar the Peaceful directed the Witenagemot at Andover that "the measure held at Winchester" should be observed throughout his realm.[10] (Some manuscripts read "at London and at Winchester".)[11][12] The statutes of William I similarly refer to and uphold the standard measures of his predecessors without naming them.

William of Malmesbury's Deeds of the Kings of England records that during the reign of Henry I "the measure of his arm was applied to correct the false ell of the traders and enjoined on all throughout England."[13] The folktale that the length was bounded by the king's nose[14] was added some centuries later. Watson dismisses William's account as "childish"[15] but William was among the most conscientious and trustworthy medieval historians,[16] the French "king's foot" was supposed to have derived from Charlemagne,[16] and the English kings subsequently repeatedly intervened to impose shorter units with the aim of increasing tax revenue.

The earliest surviving definition of this form of the ell appears in the Act on the Composition of Yards and Perches, one of the statutes of uncertain date[n 3] tentatively dated to the reign of Edward I or II c. 1300. Its wording varies in surviving accounts. One reads:[18]

It is ordained that 3 grains of barley dry and round do make an inch, 12 inches make 1 foot, 3 feet make 1 yard, 5 yards and a half make a perch, and 40 perches in length and 4 in breadth make an acre.

The Liber Horn states:[19]

And be it remembered that the iron yard of our Lord the King containeth 3 feet and no more, and a foot ought to contain 12 inches by the right measure of this yard measured, to wit, the 36th part of this yard rightly measured maketh 1 inch neither more nor less and 5 yards and a half make a perch that is 16 feet and a half measured by the aforesaid yard of our Lord the King.

In some early books, this act was appended to another statute of uncertain date titled the Statute for the Measuring of Land. The act was not repealed until the Weights and Measures Act of 1824.[21]

Yard and inch

In a law of 1439 (18 Henry VI. Cap. 16.) the sale of cloth by the "yard and handful" was abolished, and the "yard and inch" instituted.[22]

There shall be but one Measure of Cloth through the Realm by the Yard and the Inch, and not by the Yard and Handful, according to the London Measure.

According to Connor,[23] cloth merchants had previously sold cloth by the yard and handful to evade high taxes on cloth (the extra handful being essentially a black-market transaction). Enforcement efforts resulted in cloth merchants switching over to the yard and inch, at which point the government gave up and made the yard and inch official. In 1552, the yard and inch for cloth measurement was again sanctioned in law (5 & 6 Edward VI Cap. 6. An Act for the true making of Woolen Cloth.)[24]

"XIV. And that all and every Broad Cloth and Clothes called Taunton Clothes, Bridgwaters, and other Clothes which shall be made after the said Feast in Taunton, Bridgwater or in other Places of like Sort, shall contain at the Water in Length betwixt twelve and thirteen Yards, Yard and Inch of the Rule, and in Breadth seven Quarters of a Yard: (2) And every narrow Cloth made after the said Feast in the said Towns or elsewhere of like Sorts, shall contain in the Water in Length betwixt three and twenty and five and twenty Yards, Yard and Inch as is aforesaid, and in Breadth one Yard of like Measure; (3) and every such Cloth, both Broad and Narrow being well scowred, thicked, milled and fully dried, shall weigh xxxiv. li. the Piece at the least."
"XV. And that all Clothes named Check-Kersie and Straits, which shall be made after the said Feast shall contain being wet between seventeen and eighteen Yards, with the Inches as is aforesaid, and in Breadth one Yard at the least at the Water; and being well scowred, thicked, milled and fully dried, shall weigh xxiv. li. the Piece at the least."

And once in legislation of 1557-8 (4 & 5 Philip and Mary Cap. 5. An act touching the making of woolen clothes. par. IX.)[25]

"IX. Item, That every ordinary kersie mentioned in the said act shall contain in length in the water betwixt xvi. and xvii. yards, yard and inch; and being well scoured thicked, milled, dressed and fully dried, shall weigh nineteen pounds the piece at the least:..."

As recently as 1593 we find the same principle mentioned once again (35 Elizabeth. Cap. 10. An act for the reformation of sundry abuses in clothes, called Devonshire kerjies or dozens, according to a proclamation of the thirty-fourth year of the reign of our sovereign lady the Queen that now is. par. III.)[26]

"(2) and each and every of the same Devonshire kersies or dozens, so being raw, and as it cometh forth off the weaver's loom (without racking, stretching, straining or other device to encrease the length thereof) shall contain in length between fifteen and sixteen yards by the measure of yard and inch by the rule,..."

Physical standards

One of the oldest yard-rods in existence is the clothyard of the Worshipful Company of Merchant Taylors. It consists of a hexagonal iron rod 5⁄8 inch in diameter and 1⁄100 inch short of a yard, encased within a silver rod bearing the hallmark 1445.[23][27] In the early 15th century, the Merchant Taylors Company was authorized to "make search" at the opening of the annual St. Bartholemew's Day Cloth Fair.[28][29] In the mid-18th century Graham compared the standard yard of the Royal Society to other existing standards. These were a "long-disused" standard made in 1490 during the reign of Henry VII,[30] and a brass yard and a brass ell from 1588 in the time of Queen Elizabeth and still in use at the time, held at the Exchequer;[31] a brass yard and a brass ell at the Guildhall; and a brass yard presented to the Clock-Makers' Company by the Exchequer in 1671. The Exchequer yard was taken as "true"; the variation was found to be +1⁄20 to −1⁄15 of an inch, and an additional graduation for the Exchequer yard was made on the Royal Society's standard. In 1758 the legislature required the construction of a standard yard, which was made from the Royal Society's standard and was deposited with the clerk of the House of Commons; it was divided into feet, one of the feet into inches, and one of the inches into tenths. A copy of it, but with upright cheeks between which other measuring rods could be placed, was made for the Exchequer for commercial use.[32][33]

19th-century Britain

Following Royal Society investigations by John Playfair, Hyde Wollaston and John Warner in 1814 a committee of parliament proposed defining the standard yard based upon the length of a seconds pendulum. This idea was examined but not approved.[34] The Weights and Measures Act of 1824 (5° George IV. Cap. 74.) An Act for ascertaining and establishing Uniformity of Weights and Measures stipulates that:[35]

From and after the First Day of May One thousand eight hundred and twenty five the Straight Line or Distance between the Centres of the Two Points in the Gold Studs of the Straight Brass Rod now in the Custody of the Clerk of the House of Commons whereon the Words and Figures "Standard Yard 1760" are engraved shall be and the same is hereby declared to be the original and genuine Standard of that Measure of Length or lineal Extension called a Yard; and that the same Straight Line or Distance between the Centres of the said Two Points in the said Gold Studs in the said Brass Rod the Brass being at the Temperature of Sixty two Degrees by Fahrenheit's Thermometer shall be and is hereby denominated the Imperial Standard Yard and shall be and is hereby declared to be the Unit or only Standard Measure of Extension, wherefrom or whereby all other Measures of Extension whatsoever, whether the same be lineal, superficial or solid, shall be derived, computed and ascertained; and that all Measures of Length shall be taken in Parts or Multiples, or certain Proportions of the said Standard Yard; and that One third Part of the said Standard Yard shall be a Foot, and the Twelfth Part of such Foot shall be an Inch; and that the Pole or Perch in Length shall contain Five such Yards and a Half, the Furlong Two hundred and twenty such Yards, and the Mile One thousand seven hundred and sixty such Yards.

In 1834, the primary Imperial yard standard was partially destroyed in a fire known as the Burning of Parliament. In 1838, a commission was formed to reconstruct the lost standards, including the troy pound, which had also been destroyed.[36] In 1845, a new yard standard was constructed based on two previously existing standards known as A1 and A2, both of which had been made for the Ordnance Survey, and R.S. 46, the yard of the Royal Astronomical Society. All three had been compared to the Imperial standard before the fire. The new standard was made of Baily's metal No. 4 consisting of 16 parts copper, 2+1⁄2 parts tin, and 1 part zinc. It was 38 inches long and 1 inch square. The Weights and Measures Act of 1855 granted official recognition to the new standards. Between 1845 and 1855 forty yard standards were constructed, one of which was selected as the new Imperial standard. Four others, known as Parliamentary Copies, were distributed to The Royal Mint, The Royal Society of London, The Royal Observatory at Greenwich, and the New Palace at Westminster, commonly called the Houses of Parliament.[37] The other 35 yard standards were distributed to the cities of London, Edinburgh, and Dublin, as well the United States and other countries (although only the first five had official status).[38] The imperial standard received by the United States is known as "Bronze Yard No. 11"[39]

The Weights and Measures Act 1878 confirmed the status of the existing yard standard, mandated regular intercomparisons between the several yard standards, and authorized the construction of one additional Parliamentary Copy (made in 1879 and known as Parliamentary Copy VI).[40]

Definition of the yard in terms of the meter

The yard is equal to 3 feet or 36 inches. Under an agreement in 1959 between Australia, Canada, New Zealand, South Africa, the United Kingdom and the United States, the yard (known as the "international yard" in the United States) was legally defined to be exactly 0.9144 meters.[41]

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.[42] [43] The international prototype meter, on the other hand, was comparatively stable. A measurement made in 1895 determined the length of the meter at 39.370113 inches relative to the imperial standard yard. The Weights and Measures (Metric) Act of 1897[44] 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 36⁄39.370113 of a meter.

In 1959, the USA, UK, Canada, Australia, New Zealand, and South Africa agreed to adopt the international yard of exactly 0.9144 meters. In the UK, the provisions of the treaty were ratified by the Weights and Measures Act of 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.[45]

Schedule 2, Part I of The Weights and Measures Act of 1985 defines the yard as 0.9144 meters, and the meter as the distance light travels in 1⁄299792458 of a second. It then goes on to state:

Description of United Kingdom primary standard of the yard A solid bronze bar, about 38 inches long and about 1 inch square in transverse section, marked “Copper 16 oz. Tin 2+1⁄2 Zinc 1 Mr. Baily’s Metal No. 1 STANDARD YARD at 62°·00 Faht. Cast in 1845 Troughton & Simms, LONDON
Part V Authorised copies of United Kingdom primary standards of the yard and pound ... (e) a bronze bar marked “Copper 16 oz. Tin 2½ inc 1.[46]

Current use

The yard is used as the standard unit of field-length measurement in American,[47] Canadian[48] and Association football,[49] cricket pitch dimensions,[50] and in some countries, golf fairway measurements.

There are corresponding units of area and volume: the square yard and cubic yard respectively. These are sometimes referred to simply as "yards" when no ambiguity is possible, for example an American or Canadian concrete mixer may be marked with a capacity of "11 yards" or "1.5 yards", where cubic yards are obviously referred to.

Yards are also used and are the legal requirement on road signs for shorter distances in the United Kingdom, they are also frequently found in conversation between Britons much like in the United States for distance. .[51]

Textiles and fat quarters

The yard, subdivided into eighths, is used for the purchase of fabrics in the United States and United Kingdom[52] and was previously used elsewhere. In the United States the term "fat quarter" is used for a piece of fabric which is half a yard in length cut from a roll and then cut again along the width so that it is only half the width of the roll, thus the same area as a piece of one quarter yard cut from the full width of the roll; these pieces are popular for patchwork and quilting.[53] The term "fat eighth" is also used, for a piece of one quarter yard from half the roll width, the same area as one eighth cut from the roll.[54]

Equivalences

For purposes of measuring cloth, the early yard was divided by the binary method into two, four, eight and sixteen parts.[55] The two most common divisions were the fourth and sixteenth parts. The quarter of a yard was known as the "quarter" without further qualification, while the sixteenth of a yard was called a nail.[56] The eighth of a yard was sometimes called a finger,[57] but was more commonly referred to simply as an eighth of a yard, while the half-yard was called "half a yard".[58]

Other units related to the yard, but not specific to cloth measurement: two yards are a fathom, a quarter of a yard (when not referring to cloth) is a span.[59]

Conversions

  • international yard (defined 1959):[60][61]
1 yard = 0.9144 meter.[62]
1 statute mile (international mile) = 8 furlongs = 80 chains = 1760 yards
  • pre-1959 US yard - defined 1869, implemented 1893[63]
For survey purposes, certain pre-1959 units were retained, usually prefaced by the word "survey," among them the survey inch, survey foot, and survey mile, also known as the statute mile. The rod and furlong exist only in their pre-1959 form and are thus not prefaced by the word "survey." However, it is not clear if a "survey yard" actually exists.[64] If it did, its hypothetical values would be as follows:
3937 survey yard = 3600 meters[63]
1 survey yard ≈ 0.914 401 83 meter[63]
0.999 998 survey yard = 1 yard (exact)[63]
1 statute mile (US survey mile) = 8 furlongs = 80 chains = 1760 survey yards (about 1.000002 international miles)

See also

Notes

  1. ^ The later Latin gloss virgata terre describes it as "branched".
  2. ^ Middle English: Thanne drowe I me amonges draperes · my donet to lerne / To drawe þe lyser alonge [·] þe lenger it semed / Amonge þe riche rayes · I rendred a lessoun / To broche hem with a bat-nedle · and plaited hem togyderes / And put hem in a presse · and pyned hem þerinne / Tyl ten ȝerdes or twelue · tolled out threttene[[#cite_note-FOOTNOTELangland1377Ch.&nbsp;5,_<abbr_title="'"`UNIQ--nowiki-00000014-QINU`"'">ll.</abbr>&nbsp;211-216-7|[6]]]
    "Then tarried I amongst drapers · my grammar to learn; /To draw the selvedge along · the longer it seemed; /Among the rich ranged cloths · rendered a lesson, / To pierce them with a pack-needle · and plait them together, / Put them in a press · and pin them therein / Till ten yards or twelve · had tolled out to thirteen.[7]
  3. ^ Although not originally statutes, the statutes of an uncertain date were eventually accepted as such with the passage of time.

References

Citations

  1. ^ Bennett (2004), p. 8.
  2. ^ Ewart (1862), pp. 112–113.
  3. ^ a b c d OED (1921), "yard, n.2".
  4. ^ a b Thorpe (1840), p. 63.
  5. ^ Matt. xi. 7.
  6. [[#cite_ref-FOOTNOTELangland1377Ch.&nbsp;5,_<abbr_title="'"`UNIQ--nowiki-00000014-QINU`"'">ll.</abbr>&nbsp;211-216_7-0|^]] Langland (1377), Ch. 5, ll. 211-216.
  7. ^ Attwater (1957), p. 38.
  8. ^ OED (2011), "yard, n.1".
  9. ^ OED (2011), "gird, v.1".
  10. ^ Thorpe (1840).
  11. ^ Thorpe (1840), p. 113.
  12. ^ Liebermann (1903), p. 204–206.
  13. ^ Giles 1866, p. 445.
  14. ^ Green (1986), p. 106.
  15. ^ Watson (1910), pp. 36–39.
  16. ^ a b Connor (1987), p. xxiv.
  17. ^ Ruffhead (1765), p. 421.
  18. ^ BL Cotton MS Claudius D2, cited and translated in Ruffhead.[17]
  19. ^ Fowler (1884), p. 276.
  20. ^ Statutes (1824), p. 349.
  21. ^ 5 George IV C. 74, §24.[20]
  22. ^ Statutes at Large. 1763. p. 594. Retrieved 8 January 2012.
  23. ^ a b Connor (1987).
  24. ^ Owen Ruffhead, ed. (1763). The statutes at large. Vol. 2. p. 442. Retrieved 29 February 2012.
  25. ^ Great Britain; Pickering, Danby (1763). Danby Pickering (ed.). The statutes at large. Vol. 6. Printed by J. Bentham. p. 96. Retrieved 29 February 2012.
  26. ^ Great Britain; Pickering, Danby (1763). The statutes at large. Vol. 6. Printed by J. Bentham. p. 444. Retrieved 29 February 2012.
  27. ^ Robinson, Sir John Charles; Victoria and Albert museum (1863). Catalogue of the special exhibition of works of art of the mediæval, Renaissance, and more recent periods, on loan at the South Kensington museum, June 1862. Printed by George E. Eyre and William Spottiswoode, printers to the Queen's most excellent Majesty. For Her Majesty's Stationery Office. p. 452. Retrieved 22 February 2012.
  28. ^ William Carew Hazlitt (1892). The livery companies of the city of London: their origin, character, development, and social and political importance. S. Sonnenschein & co. p. 280. Retrieved 22 February 2012.
  29. ^ Clode, Charles Mathew (1888). The early history of the Guild of merchant taylors of the fraternity of St. John the Baptist, London: with notices of the lives of some of its eminent members. Harrison. p. 128. Retrieved 22 February 2012.
  30. ^ Great Britain. Parliament. House of Commons (1873). Reports from commissioners. Vol. 38. House of Commons. p. 34. Retrieved 8 January 2012.
  31. ^ Great Britain. Parliament. House of Commons (1873). Reports from commissioners. Vol. 38. House of Commons. pp. 25–6. Retrieved 8 January 2012.
  32. ^ Knight, Charles (1840). The Penny magazine of the Society for the Diffusion of Useful Knowledge, Volume 9. London: Society for the Diffusion of Useful Knowledge. pp. 221–2.
  33. ^ Herbert Treadwell Wade (1905). The New international encyclopaedia. Dodd, Mead and company. p. 405. Retrieved 8 January 2012.
  34. ^ Charles Hutton Dowling (1872). A series of metric tables: in which the British standard measures and weights are compared with those of the metric system at present in use on the continent. Lockwood. pp. xii–iii. Retrieved 8 January 2012.
  35. ^ Great Britain (1824). The statutes of the United Kingdom of Great Britain and Ireland (1807-1865). His Majesty's statute and law printers. pp. 339–354. Retrieved 31 December 2011.
  36. ^ Connor 1987, p. 261.
  37. ^ Ronald Edward Zupko (1990). Revolution in measurement: Western European weights and measures since the age of science. American Philosophical Society. p. 183. ISBN 978-0-87169-186-6. Retrieved 22 January 2012.
  38. ^ Connor 1987, p. 264–266.
  39. ^ NIST museum collection
  40. ^ Great Britain (1878). Statutes at large. pp. 308–341. Retrieved 31 December 2011.
  41. ^ 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 a.m.)
  42. ^ "History Of Calibration". Norwich Instrument Services. 2012. Retrieved 25 April 2012.
  43. ^ "The Gauge Block Handbook" (PDF). The National Institute of Standards and Technology (NIST). 2013. Retrieved 16 November 2013.
  44. ^ John Mews, ed. (1897). "Statutes of the Realm - 60-61 Victoria". The Law journal reports. Vol. 66. London: The Law Journal Reports. p. 109. Retrieved 16 September 2012.
  45. ^ Ronald Edward Zupko (1990). Revolution in measurement: Western European weights and measures since the age of science. American Philosophical Society. p. 432. ISBN 978-0-87169-186-6. Retrieved 22 January 2012.
  46. ^ 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
  47. ^ American Football pitch dimensions
  48. ^ Canadian Football Pitch dimensions
  49. ^ Association Football pitch dimensions,
  50. ^ Cricket pitch dimensions
  51. ^ Driving Standards Agency (1999), The Highway Code, London: The Stationery Office, ISBN 0-11-551977-7, pp. 74–75
  52. ^ "S0733: Frozen pattern". Simplicity New Look. Retrieved 1 January 2015. The pattern envelope shows the fabric requirements in yards and eighths, in English, and in metric measurements, in French.
  53. ^ Penn, Sue (2006). "What are Fat Quarters?". Fat Quarter Quilting. Krause Publications Craft. ISBN 9780896891715.
  54. ^ Yoder, Corey (2014). "Fat Eighth Bundles". Playful Petals: Learn Simple, Fusible Appliqué. C&T Publishing. p. 23. ISBN 9781607057987. Retrieved 1 January 2015.
  55. ^ The statutes at large. 1763. p. 631. Retrieved 26 January 2012.
  56. ^ Charles Arnold (1850). The boy's arithmetic. p. 54. Retrieved 26 January 2012.
  57. ^ The Encyclopedia Americana. Encyclopedia Americana Corp. 1920. p. 165. Retrieved 14 January 2012.
  58. ^ Instructions for cutting out apparel for the poor. Sold by J. Walter. 1789. p. 53. Retrieved 26 January 2012.
  59. ^ Isaiah Steen (1846). A treatise on mental arithmetic, in theory and practice. p. 9. Retrieved 27 January 2012.
  60. ^ Donald Fenna (26 October 2002). A dictionary of weights, measures, and units. Oxford University Press. pp. 130–1. ISBN 978-0-19-860522-5. Retrieved 8 January 2012.
  61. ^ Hearst Magazines (March 1959). Popular Mechanics. Hearst Magazines. p. 248. ISSN 0032-4558. Retrieved 8 January 2012.
  62. ^ "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. Retrieved 2012-01-07.
  63. ^ a b c d NIST Guide to the SI - section B.6 U.S. survey foot and mile
  64. ^ NIST Handbook 44 - 2012 Appendix C "General Tables of Units of Measurement" page C-5

Bibliography

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