Troy-weight

troi′-wāt, n. the system of weights used in England for gold, silver, and precious stones. The troy pound contains 5760 grains, and is to the avoirdupois pound as 144 to 175, while the troy ounce is to the avoirdupois ounce as 192 to 175. [From Troyes , in France, the pound weight of which was adopted in England in the 14th century.]