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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== The name derives from the Old English ', ', &c., which was used for branches, staves, and measuring rods. It is first attested in the late-7th century laws of Ine of Wessex, where the "yard of land" mentioned is the yardland, an old English unit of tax assessment equal to hide. Around the same time, the Lindisfarne Gospel's account of the messengers from John the Baptist in the Book of Matthew〔Matt. xi. 7.〕 used it for a branch swayed by the wind. In addition to the yardland, Old and Middle English both used their forms of "yard" to denote the surveying lengths of 15 or ft used in computing acres, a distance now usually known as the "rod". A unit of three English feet is attested in (see below) but there it is called an ell ((ラテン語:ulna), "arm"), a separate and usually longer unit of around 45 inches. The use of the word "yard" (' or ') to describe this length is first attested in Langland's poem on Piers Plowman. "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.}} 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「yard」の詳細全文を読む スポンサード リンク
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