A mostly obsolete system of weights used to measure precious metals such as gold, silver, and platinum, and genstones other than diamonds. It is still in common use in the U.S. and sometimes in the U.K., but on the international market has largely been replaced with the more convenient metric system. Troy weight is often confused with Apothecaries' weight or even the Avoirdupois system; while all three are based on the same unit (the grain), the larger units differ.

The units are as follows:

The result is that one Troy ounce is approximately 1.095 ounces Avoirdupois, and one Troy pound approximately 0.82 pounds Avoirdupois. The pennyweight was once the British standard for the weight of a silver penny.

The origin of the name is debatable. According to common legend, it was brought to Europe by returning Crusaders in Troyes, France. However, the actual origin is probably in London, which used to be called Troy-Novant.

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