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
Exchequer Standards inches. According to Secretary Adams, Adams goes on to say (paraphrased and simplified): Thus, the key to the whole measurement system of 1266 was the weight of the silver penny sterling. This penny was 1/240th of the Tower pound, which had been used at the London mint for centuries before the Norman conquest, and which continued as legal tender until 1527, when Henry VIII replaced it with the Troy pound. The Tower pound weighed 3/4 Troy ounce less than the Troy pound (15/16th of the Troy pound). Its penny, therefore weighed 22.5 Troy grains. There was also another pound used