The majority of U.S. customary units were redefined in terms of the meter and the kilogram with the Mendenhall Order of 1893 and, in practice, for many years before.[1] These definitions were refined by the international yard and pound agreement of 1959.[2]
Americans primarily use customary units in commercial activities, as well as for personal and social use. In science, medicine, many sectors of industry, and some of government and military, metric units are used. The International System of Units (SI), the modern form of the metric system, is preferred for many uses by the U.S. National Institute of Standards and Technology (NIST).[3] For newer units of measure where there is no traditional customary unit, international units are used, sometimes mixed with customary units, such as electrical resistance of wire expressed in ohms (SI) per thousand feet.