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The basic unit of length in the imperial and U.S. customary systems is the yard, defined as exactly 0.9144 m by international treaty in 1959. [2] [10] Common imperial units and U.S. customary units of length include: [11] thou or mil (1 ⁄ 1000 of an inch) inch (25.4 mm) foot (12 inches, 0.3048 m) yard (3 feet, 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 (16.66 °C).
Miners also use it as a unit of area equal to 6 feet square (3.34 m 2) in the plane of a vein. [2] In Britain, it can mean the quantity of wood in a pile of any length measuring 6 feet (1.8 m) square in cross section. [2] In Central Europe, the klafter was the corresponding unit of comparable length, as was the toise in France.
The rod, perch, or pole (sometimes also lug) is a surveyor's tool [1] and unit of length of various historical definitions. In British imperial and US customary units, it is defined as 16 + 1 ⁄ 2 feet, equal to exactly 1 ⁄ 320 of a mile, or 5 + 1 ⁄ 2 yards (a quarter of a surveyor's chain), and is exactly 5.0292 meters.
For measuring length, the U.S. customary system uses the inch, foot, yard, and mile, which are the only four customary length measurements in everyday use.From 1893, the foot was legally defined as exactly 1200 ⁄ 3937 m (approximately 0.304 8006 m). [13]
In 1893 the United States fixed the yard at 3600 ⁄ 3937 metres, making the yard 0.9144018 metres and 1896 the British authorities fixed the yard as being 0.9143993 metres. [ citation needed ] At the time the discrepancy of about two parts per million was considered to be insignificant.
One acre equals 1 ⁄ 640 (0.0015625) square mile, 4,840 square yards, 43,560 square feet, [2] or about 4,047 square metres (0.4047 hectares) (see below).While all modern variants of the acre contain 4,840 square yards, there are alternative definitions of a yard, so the exact size of an acre depends upon the particular yard on which it is based.
4,047 m 2: An area of land one chain (four rods) wide by one furlong in length. As the traditional furlong could vary in length from country to country, so did the acre. In England an acre was 4,840 square yards (4,050 m 2), in Scotland 6,150 square yards (5,140 m 2) and in Ireland 7,840 square yards (6,560 m 2). It is a Saxon unit, meaning ...