In the 1950s, the United States entered into an international agreement that unified length and mass/weight units in the United States and Commonwealth of Nations. A single yard and pound became the official units of that name under this agreement, coming into force in the United States on July 1, 1959, and in the United Kingdom in 1963. Under this agreement, 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 International yard was 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. See Survey foot.)