In 1866, after most of the South American countries started to use the metric system, the United States passed a law that allowed people to use either the metric system or United States customary units for trade. Before 1893 the yard was defined as the length of the "standard yard" which was kept by the United States Treasury. The pound was defined as being the mass of the "standard pound". In 1893 the United States Congress passed the Mendenhall Order. This order defined the yard as being exactly metres and the pound as being exactly 0.4535924277 kilogram. The order only changed the definitions of the pound and the yard. It had no other effect on people's lives.