Unit of length

[1][2][3] Before the establishment of the decimal metric system in France during the French Revolution in the late 18th century,[4] many units of length were based on parts of the human body.

Other SI units are derived from the meter by adding prefixes, as in millimeter or kilometer, thus producing systematic decimal multiples and submultiples of the base unit that span many orders of magnitude.

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] In addition, the following are used by sailors: Aviators use feet for altitude worldwide (except in Russia and China) and nautical miles for distance.

[12][13] American surveyors use a decimal-based system of measurement devised by Edmund Gunter in 1620.