Troy Weight
3 of the 7 encyclopedias on this shelf carry an entry for Troy Weight. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a system of measures used in weighing precious metals. In the Middle Ages each commercial city had its official measures, as the foot, gallon, pound, etc. Troyes, a city of some importance, situated southeast of Paris, was one of these. Among the local measures that have survived and have acquired national and even international acceptance are the Winchester bushel and, it is believed, the pound of Troyes, or the pound troy, as it came to be known. It had been for some time the standard of weight for silver spoons, etc., but in 1527 it was made the basis of English coinage. It was for a time the standard of weight in England for bread, silk, and jewelry as well. The pound troy contains 12 ounces, or 240 pennyweights, or 5,760 grains. The pound avoirdupois contains 7,000 grains troy. See Avoirdupois
Collier's New Encyclopedia (1921)
a system of weights used for gold, silver, platinum, and precious stones. The Troy pound contains 12 ounces, 240 pennyweights, and 5,760 grains, being thus less than the avoirdupois pound, which contains 7,000 grains. The old apothecary's weight, which had the same value of pound as the Troy, but subdivided into 12 ounces, 96 drachms, and 288 scruples, was abolished in Great Britain and the new apothecary's weight made the same as the avoirdupois. The name Troy was given to the standard pound in 1495. The origin of the name is doubtful, some deriving it from "Troy Novant," the monkish name of London, others from Troyes in France.
The Encyclopedia of Founding (1892)
A weight used chiefly in weighing the precious metals, gems, jewelry, etc. A standard pound Troy contains twelve ounces, each ounce twenty pennyweights, and each pennyweight twenty-four grains.