Troy Ounce (ozt)

The precious metal ounce of 480 grains, descended from the weights used at the medieval fairs of Troyes in Champagne.

The troy ounce is the most commercially significant unit in this archive, and almost nobody handles one. Every price quoted for gold, silver, platinum and palladium on every exchange in the world is per troy ounce, which makes a medieval French fair weight the basis of a market running to trillions. It is heavier than the ordinary avoirdupois ounce by about ten per cent, 480 grains against 437.5, which is the source of the old riddle about gold and feathers: the troy ounce is heavier, but the troy pound is lighter, because it holds only twelve ounces where the ordinary pound holds sixteen. Britain abolished troy weight for trade in 1878 and made a single exception for the ounce, which is why it survives alone, without the pound and pennyweight that once sat above and below it.