Coins of the pound sterling another silver coin, the sceat, of 20 troy grains weight, which was in general circulation in Europe during the Middle Ages. The weight of the English penny was fixed at troy grains (about 1.46 grams) by Offa of Mercia, an 8th-century contemporary of Charlemagne. The coin's designated value, however, was that of 24 troy grains of silver (one pennyweight, or of a troy pound, or about 1.56 grams), with the difference being a premium attached by virtue of the minting into coins. Thus, 240 pennyweights made one troy pound of silver in weight, and the monetary value of 240 pennies
Troy weight Congress on May 19, 1828. The British Imperial troy ounce (known more commonly simply as the imperial troy ounce) was based on, and virtually identical with, the pre-1824 British troy ounce and the pre-1707 English troy ounce. (1824 was the year the British Imperial system of weights and measures was adopted, 1707 was the year of the Act of Union which created the Kingdom of Great Britain.) Troy ounces have been used in England since about 1400 and the English troy ounce was officially adopted for coinage in 1527. Before that time, various sorts of troy ounces were in use