Metallurgy Question:

Troy ounce defined by the troy system of mass. In troy weight, there are 12 ounces in a pound, and a troy pound is 5760 grains (about 373.24 g), rather than 7000 (about 453.59 g). Note: at roughly 31.10 g, the troy ounce is about 10 per cent more than the more-common avoirdupois ounce. These troy ounces are now used only when weighing precious metals like gold and silver. One ounce of gold is always 31.1 g.