This article is about post-1824 imperial units, see also English unit, U.S. customary units or Avoirdupois.Imperial units or the Imperial system is a collection of units, first defined in the British Weights and Measures Act of 1824, later refined (until 1959) and reduced. The units were introduced in the United Kingdom and its colonies, including Commonwealth countries (most have since become officially metric), but excluding the then already independent United States. Systems of imperial units are sometimes referred to as foot-pound-second, after the base units of length, mass and time.
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