The pound or pound-mass is a unit of mass used in the imperial, United States customary and other systems of measurement. The avoirdupois pound, also known as the wool pound, first came into general use (circa) 1300. It was initially equal to 6992 troy grains. The pound avoirdupois was divided into 16 ounces. During the reign of Queen Elizabeth, the avoirdupois pound was redefined as 7,000 troy grains. Since then, the grain has often been an integral part of the avoirdupois system. In the US, the avoirdupois pound as a unit of mass has been officially defined in terms of the kilogram since the Mendenhall Order of 1893. That Order defined the pound to be 2.20462 pounds to a kilogram. The following year this relationship was refined as 2.20462234 pounds to a kilogram, following a determination of the British pound. According to a 1959 NIST publication, the US 1894 pound differed from the international pound by approximately one part in 10 million. The difference is so insignificant that it can be ignored for almost all practical purposes