On July 1, 1959, the units of length in the United States and the Commonwealth of Nations were altered to become identical to the units which had, up to then, been adopted in Canada. The new units were all defined in terms of the International yard, defined as exactly 0.9144 m, slightly shorter than the previous definition in the United States, but slightly longer than the previous definition in the United Kingdom. (The differences were of the order of parts per million, and therefore to all intents and purposes were identical. But where extreme precision was wanted, the difference was accounted for.)

The International foot was in turn defined as ⅓ of the International yard, which makes it exactly 0.3048 m. The previous United States customary foot and British Imperial foot were revised to correspond to the new definitions, although the old value of the U. S. customary foot was retained, under the name of the Survey foot, as a unit used on older maps which had been surveyed under the former standard.

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