GNU Collaborative International Dictionary of English
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Troy , n. Troy weight.1913 Webster
Troy weight, the weight which gold and silver, jewels, and the like, are weighed. It was so named from Troyes, in France, where it was first adopted in Europe. The troy ounce is supposed to have been brought from Cairo during the crusades. In this weight the pound is divided into 12 ounces, the ounce into 20 pennyweights, and the pennyweight into 24 grains; hence, the troy ounce contains 480 grains, and the troy pound contains 5760 grains. The avoirdupois pound contains 7000 troy grains; so that 175 pounds troy equal 144 pounds avoirdupois, or 1 pound troy = 0.82286 of a pound avoirdupois, and 1 ounce troy = 1¹⁷⁄₁₇₅ or 1.09714 ounce avoirdupois. Troy weight when divided, the pound into 12 ounces, the ounce into 8 drams, the dram into 3 scruples, and the scruple into 20 grains, is called apothecaries' weight, used in weighing medicines, etc. In the standard weights of the United States, the troy ounce is divided decimally down to the ¹⁄₁₀₀₀₀ part.
1913 Webster