Foot (unit of length)

From Recruitiki

A foot (plural: feet or foot;<ref>BBC World Service</ref> symbol or abbreviation: ft or, sometimes, ′ – a prime) is a unit of length, in a number of different systems, including English units, Imperial units, and United States customary units. Its size can vary from system to system, but in each is around a quarter to a third of a metre. The most commonly used foot today is the international foot. There are 3 feet in a yard and 12 inches in a foot.

Definition

International foot

In 1958 the United States and countries of the Commonwealth of Nations defined the length of the international yard to be 0.9144 metres. Consequently, the international foot is defined to be equal to 0.3048 metres (equivalent to 304.8 millimetres).

The international standard symbol for a foot is "ft" (see ISO 31-1, Annex A). In some cases, the foot is denoted by a prime, which is often approximated by an apostrophe, and the inch by a double prime. For example, 5 feet 2 inches is denoted by 5′2″. This use can cause confusion, because the prime and double prime are also international standard symbols for arcminutes and arcseconds.

United States survey foot

The United States survey foot is defined as exactly Template:Fraction metres, approximately 0.30480061 m. It is used only in connection with surveys by the U.S. Coast and Geodetic Survey. It is 610 nm greater than the international foot. <ref>A. V. Astin & H. Arnold Karo, (1959), Refinement of values for the yard and the pound, Washington DC: National Bureau of Standards, republished on National Geodetic Survey web site and the Federal Register (Doc. 59-5442, Filed, June 30, 1959, 8:45 a.m.)</ref> The U.S. Survey Foot is used by Land Surveyors and other cartographers for the plans and maps they produce. Each state has a law that states which form of the foot is used for surveys within the given state. The difference is particularly noticeable when converting coordinates that are on the State Plane Coordinate System of the given state.