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The U.S. Customary System

The weights and measures in common use in the American colonies at the time of the American Revolution were all of English origin and were the same as those then used in Great Britain.

The following units are still in use in the United States: (a) the yard of 35 inches, (b) the avoirdupois pound of 7,000 grains, (c) the gallon of 231 cubic inches, and (d) the winchester bushel (or simply bushel) of 2,150.42 cubic inches.

In 1893, after receipt of the metric standards, it was decided that a more stable basis for the system of customary weights and measures in the United States would be obtained by defining the yard in terms of the metre and the pound in terms of the kilogram using the U.S. prototype metre and the U.S. prototype kilogram, respectively, with their certified corrections as the primary standards of length and mass in this country. This is the present basis of the units.

The U.S. yard is defined as 3.600/3.937 metre and the U.S. pound as 0.4535924277 kilogram.

For industrial purposes, in the conversion of inches to millimetres and millimetres to inches, a relation between the inch and the millimetre has been adopted by the American Standard Association (1933) and by similar organizations in other countries.

This relation is

1 inch = 25.4 millimetres (exactly)

whereas the relation 1 U.S. yard = 3.600/3.937 = metre gives

1 inch = 25.4000508 millimetres.

It is to be noted that although the mass of a body, often de­fined as the quantity of matter in a body, remains constant everywhere and under all conditions as long as no portion of the body is taken away and no matter added to it, its weight, being a force equal to the product of mass of the body by the acceleration of gravity, varies with the locality in which it is measured [2, С. 40 - 41].

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