The system for measuring length in the United States customary system is based on the:
inch, Foot, Yard, and Mile.
Which are the only four customary length measurements in everyday use.
Since July 1, 1959, these have been defined on the basis of 1 yard = 0.9144 meters except for some applications in surveying.
This definition was agreed with the UK and other Commonwealth countries, and so is often termed international measure.
When international measure was introduced in the English-
This definition was retained for data derived from NAD27, but renamed the US survey foot to distinguish it from the international foot.
For most applications, the difference between the two definitions is insignificant, one international foot is exactly 0.999998 of a US survey foot, for a difference of about 1⁄8 inch (3 mm) per mile, but it affects the definition of the State Plane Coordinate Systems (SPCSs), which can stretch over hundreds of miles.
The NAD27 was replaced in the 1980's by the North American Datum of 1983 (NAD83), which is defined in meters.
The SPCSs were also updated, but the National Geodetic Survey left the decision of which (if any) definition of the foot to use to the individual states.
All SPCSs are defined in meters, but seven states also have SPCSs defined in US survey feet and an eighth state in international feet: the other 42 states use only meter-
State legislation is also important for determining the conversion factor to be used for everyday land surveying.
Eight have legislated that they be made on the basis of the international foot.
Eighteen have not specified the conversion factor from metric units.
This will not normally affect modelling scales but is use full information to know when documenting and reading full scale US Drawings and Diagrams.
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Without distinguishing it from the tonne (1,000 kilograms or 2,204.62262 pounds, known there as the "metric ton"), or the long ton (2,240 pounds or 1,016.0469088 kilograms, known there as the "Imperial ton").
When one of the latter two are intended, they are specifically noted. There are, however, some U.S. applications for which unspecified tons normally means long tons (for example, Navy ships) or metric tons (world grain production figures).
Both the long and short ton are defined as 20 hundredweights, but a hundredweight is 100 pounds (45.359237 kg) in the U.S. system (short or net hundredweight) and 112 pounds (50.80234544 kg) in the imperial system (long or gross hundredweight).