The units described in this article are those implemented in the United States on July 1, 1959, when a new definition took effect by law, and in the United Kingdom in 1963, with a Weights and Measures Act of that year, as a result of an agreement between the United States and the nations of the Commonwealth of Nations. Because of this agreement, they are properly described as International, although in all countries other than the United States they have been phased out in favor of the metric system ({{International System of Units]], abbreviated SI from its French designation).