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The imperial and US customary systems of measurement are two closely inter-related systems of measurement both derived from earlier English system of measurement units which can be traced back to Ancient Roman units of measurement, and Carolingian and Saxon units of measure. US Customary units, developed and used in the United States after the American Revolution, are based on a subset of the English units used in the Thirteen Colonies, while the Imperial system of units was developed and used after 1824 in the United Kingdom and subsequently used in the rest of the Commonwealth. US Customary units are the predominant system of units in the United States, but in all Commonwealth countries the metric system has, to varying degrees, replaced the imperial system. Most of the units of measure have been adopted in one way or another since the Norman Conquest (1066). The units of linear measure have changed the least – the yard (which replaced the ell) and the chain were measures derived in England. The foot used by craftsman supplanted the foot used in agriculture which was reduced in size by a factor of to bring it into alignment. This resulted in there being feet in a rod, pole or perch instead of 15 agricultural feet. The furlong and the acre, once it became a unit of the size of a piece of land rather than its value, remained relatively unchanged. In the last thousand years, three principal pound were used in England. The troy pound (5760 grains) was used for precious metals, the apothecaries' pound, (also 5760 grains) was used by pharmacists and the avoirdupois pound (7000 grains) was used for general purposes. The apothecaries and troy pounds are divided into 12 ounces (of 480 grains) while the avoirdupois pound has 16 ounces (of 437.5 grains). The unit of volume, the gallon, has different values in the United States and in the United Kingdom – the US fluid gallon being about 0.83 imperial gallons and the US dry gallon being about 0.89 imperial gallons. Both systems of measure were widely used in mechanical engineering, though not in electrical engineering. Some units of measure such as the horsepower or the British thermal unit (BTU) have special names but by and large unit names are generated from their constituent components – for example, pounds per square inch. In contrast, the metric system has a special name for pressure—the pascal. After the United States Declaration of Independence the units of measurement in the United States developed into what is now known as customary units. The United Kingdom overhauled its system of measurement in 1824, when it introduced the imperial system of units. This resulted in both countries having different gallons. Later in the century, efforts were made to align the definition of the pound and the yard in both countries by using copies of the standards adopted by the British Parliament in 1855. However, these standards were of poor quality compared with those produced for the Convention of the Metre. In 1960 both countries agreed to common definitions of the yard and the pound based on definitions of the metre and the kilogram. This change, which amounted to a few parts per million, had little effect in the United Kingdom, but resulted in the United States having two slightly different systems of linear measure – the international system, and the surveyors system. == English units of measure== (詳細はRoman, Carolignian and Saxon units of measure. They were a precursor to both the Imperial system of units (first defined in 1824) and United States customary units which evolved from English Units from 1776 onwards.〔 The earliest records of English units of measure relate to Saxon coinage – at that time coins were both weights and currency. The penny introduced by Offa was about 20 grains (1.296 g). Edward the Elder increased the weight of the English penny to 26 grains (1.685 g), thereby aligning it with the penny of Charlemagne, but by the time of the conquest (1066), it has decreased to 24 grains (1.555 g). This value was subsequently called the ''pennyweight'' and formed the basis of the Troy units of weight—the troy ounce being used to this day for weighting precious metals.〔 In 965 AD, King Edgar decreed "that only one weight and one measure should pass throughout the King's dominion". In his report to Congress in 1817, John Quincy Adams wrote that the link between coinage and weight (or mass) was broken during the reign of Edward I (1272–1307) when he debased the English coinage by introducing a groat (four pence) which weighed of 89 grains rather than the expected 96 grains. In the 1350s the groat was further devalued by reducing its weight to 72 grains. One of the enduring conflicts during medieval times was who had the right to define weights and measures. In 1197 Richard I decreed that the measures of corn and pulse, and of wine and ale should be the same throughout all England. The Magna Carta, signed by King John in 1215 extended this to include cloth. During Saxon times land was described in both terms of its economic value and in terms of an absolute size. In the Domesday Book, the hide, an economic unit of measure was used, while there are references elsewhere relating to the furlong and to the rood that appear to be related to ploughing procedures. Of particular interest was the rood which was 15 (German or Saxon ) feet in length, the North German foot being equivalent to 335 mm (13.2 inches).〔 Craftsmen, on the other hand used a shorter Roman foot. Some time between 1266 and 1303 the weights and measures of England were radically revised by a law known as the ''Composition of Yards and Perches'' (''Compositio ulnarum et perticarum'') often known as the ''Compositio'' for short. This law, attributed to either Henry III or his successor Edward I, instituted a new foot that was exactly the length of the old foot, with corresponding reductions in the size of the yard, ell, inch, and barleycorn. Furlongs and rods, however, remained the same, but the rod changed from 15 old feet to 16 new feet. Units of length were systematized by Edward II who in 1324 defined the inch as being three barleycorns, the foot as twelve inches, the yard as three feet, the perch five and half yards and the acre as being an area four perches in width by forty perches in length. Apart from the ell (45 inches or 114.3 cm) which continued to be used in the cloth trade and the chain which was introduced by Edmund Gunter in 1620, these units formed the basis of the units of length of the English system of measurement. The units were however redefined many times – during Henry VIII's time standard yards and ells made of brass were manufactured, during Elizabeth I's time these replaced these with standards made of bronze and in 1742, after scientific comparisons showed a variation of up to 0.2% from the mean, a definitive standard yard was proposed (but not manufactured).〔 During the medieval era agricultural products, apart from wool, were mostly sold by volume, with various bushels and gallons being introduced over the years for different commodities. In the early fourteenth century the wool trade traditionally used the avoirdupois system of weights, a process that was formalized by Edward III in 1340. At the same time, the stone, when used to weigh wool, was formalized as being 14 pounds. During the Tudor period, numerous reforms were made to English weights and measures. In 1496 Henry VII ordered that reference copies of the yard, pound and gallon should be made of brass and distributed to specified towns and cities throughout the kingdom.〔 Many weights and measures that had crept into use were banned: in 1527 Henry VIII banned the Tower pound (5400 grains against the 5760 grains of the apothecaries and troy pounds) and the mercantile pound (6750 grains against the 7000 grains of the pound avoirdupois)〔 and in 1592 Elizabeth I ordered the use of the "statute mile" (5280 feet against the 5000 feet of the London or Old English mile).〔 Under the Act of Union of 1707, Scotland, which had developed its own system of weights and measures independently of England, abandoned them in favour of English weights and measures.〔 The Acts of Union 1800 which united Ireland with Great Britain had less of an effect on weights ands measures—Irish weights and measures having been based on the English foot and pound avoirdupois since 1351, though the Irish acre and mile were based on a perch of 7 yards, not yards as in England.〔 By the early nineteenth century many commodities had their own set of units, the units of measure for the wool and cloth industries had units of measure specific to those commodities, albeit derived on the pound avoirdupois or the foot while wine and beer used units with the same names but different sizes – the wine gallon being 231 cubic inches and the beer or ale gallon being 282 cubic inches. Agricultural produce was sold by the bushel which was based on yet another gallon – the dry gallon of 268.8 cubic inches. Even though not explicitly permitted by statute, many markets used bushels based on weight rather than volume when selling wheat and barley. 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「Imperial and US customary measurement systems」の詳細全文を読む スポンサード リンク
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