The
troy ounce is the traditional unit of mass for precious
metals. It derives from the troy system of mass, which dates back to before the time of
William the Conqueror. Its name is thought to derive from the town of Troyes
? in
France. 1 troy ounce is defined as exactly 480 grains, where 1 grain is exactly 64.79891
grams.
The symbol for ounce is ℥