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In both customary and imperial units, one foot comprises 12 inches, and one yard comprises three feet. Since an international agreement in 1959 , the foot is defined as equal to exactly 0.3048 meters.
(Furlongs remained the same, but the rod changed from 15 old feet to 16 1 ⁄ 2 new feet. [10]) In 1324 Edward II systematized units of length by defining the inch as 3 barleycorns, the foot as 12 inches, the yard as 3 feet, the perch as 5 1 ⁄ 2 yards, and the acre as an area 4 by 40 perches. [2]
A child's size zero is equivalent to 4 inches (a hand = 12 barleycorns = 10.16 cm), and the sizes go up to size 13 + 1 ⁄ 2 (measuring 25 + 1 ⁄ 2 barleycorns, or 8 + 1 ⁄ 2 inches (21.59 cm)). Thus, the calculation for a children's shoe size in the UK is: child shoe size (barleycorns) = 3 × last length (in) − 12. equivalent to:
The US survey foot is defined so that 1 metre is exactly 39.37 inches, making the international foot of 0.3048 metres exactly two parts per million shorter. This is a difference of just over 3.2 mm, or a little more than one-eighth of an inch per mile.
1 ⁄ 12 of a ligne. This unit is usually called the Truchet point in English. Prior to the French Revolution the Fournier point was also in use. It was 1 ⁄ 6 of a ligne or 1 ⁄ 864 of the smaller French foot. ligne: 1 ⁄ 144: 2.256 mm 88.81 thou 1 ⁄ 12 of a pouce. This corresponds to the line, a traditional English unit. pouce: 1 ⁄ 12: ...
The prime symbol ′ is commonly used to represent feet (ft), and the double prime ″ is used to represent inches (in). [2] The triple prime ‴, as used in watchmaking, represents a ligne (1 ⁄ 12 of a "French" inch, or pouce, about 2.26 millimetres or 0.089 inches). [3] Primes are also used for angles.
This is approximately 1 / 8 inch per mile; 12.7 kilometres is exactly 500,000 standard inches and exactly 499,999 survey inches. This difference is substantial when doing calculations in State Plane Coordinate Systems with coordinate values in the hundreds of thousands or millions of feet.
There are anecdotal objections to the use of metric units in carpentry and the building trades, on the basis that it is easier to remember an integer number of inches plus a fraction, rather than a measurement in millimeters, [9] or that foot-inch measurements are more suitable when distances are frequently divided into halves, thirds, and ...