The yard (symbol: yd) is an English unit of length in both the British imperial and US customary systems of measurement equalling 3 feet or 36 inches. Since 1959 it has been by international agreement standardized as exactly 0.9144 meter. A distance of 1,760 yards is equal to 1 mile.
The US survey yard is very slightly longer.
The term, yard derives from the Old English gerd, gyrd etc., 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 Gospels account of the messengers from John the Baptist in the Gospel of Matthew 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 or , used in computing acres, a distance now usually known as the "rod".
A unit of three English feet is attested in a statute of 1300 (see below), but there it is called an ell (ulna, () "arm"), a separate and usually longer unit of around . The use of the word ‘yard’ (ȝerd or ȝerde) to describe this length is first attested in William Langland's poem on Piers Plowman. 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 word ‘garden’ and is not related to the unit of measurement.
The origin of the yard measure is uncertain. Both the Romans and the Welsh used multiples of a shorter foot, but 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 . This has led some to derive the yard of three English feet from pacing; others from the ell or cubit; and still others from Henry I's arm standard (see below).
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A system of units of measurement, also known as a system of units or system of measurement, is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Instances in use include the International System of Units or () (the modern form of the metric system), the British imperial system, and the United States customary system.
The foot ( () feet), standard symbol: ft, is a unit of length in the British imperial and United States customary systems of measurement. The prime symbol, , is a customarily used alternative symbol. In both customary and imperial units, one foot comprises 12 inches, and one yard comprises three feet. Historically, the "foot" was a part of many local systems of units, including the Greek, Roman, Chinese, French, and English systems. It varied in length from country to country, from city to city, and sometimes from trade to trade.
In metrology (the science of measurement), a standard (or etalon) is an object, system, or experiment that bears a defined relationship to a unit of measurement of a physical quantity. Standards are the fundamental reference for a system of weights and measures, against which all other measuring devices are compared. Historical standards for length, volume, and mass were defined by many different authorities, which resulted in confusion and inaccuracy of measurements.
Adiabatic pressure drop measurements of two-phase Carbon Dioxide (CO2) have been carried out in horizontal, vertical upward and downward direction with a dedicated test facility at the European Organization for Nuclear Research (CERN). A database of more t ...