Pound of 16 oz. × 8 ternau × 3 denié × 24 gran.
There we see the scruple becomes a pennyweight, and the obolus or half-scruple becomes a halfpenny.
In Northern France:
Mint-marc 8 oz. × 8 gros × 3 deniers × 24 grains.
Medicinal lb. of 12 oz. × 8 drachmes × 3 scrupules × 24 grains.
Commercial lb. of 16 oz. × 8 gros × 72 grains.
In this system, common to France, Spain, Portugal, Florence, and Rome, the ounce is divided into 576 parts or grains, while the Troy ounce of the rest of Europe is of 480 grains. This makes the Latin grain lighter.
In the medicinal pound, more or less international throughout the West, the 24 Scruples of the ounce are grouped into 8 drachms of 3 scruples.
It may be concluded that the English Troy pound was a Northern weight with its ounce of 480 instead of 576 parts. It has no direct connexion but in name with the marc of Troyes. It probably came to us as an apothecary’s and goldsmith’s pound, and in the latter, the Latin factors 24 scruples × 20 grains were transposed for mint purposes so as to preserve the ancient pennyweight 1/20 ounce of the Tower pound. But in the apothecary’s Troy pound the ounce remained divided into 24 scruples (8 drachms of 3 scruples) each of 20 grains as in other countries except France, &c.
The story of the goldsmiths’ Carat and Grain will be found in [Chapter XX], that of the Provençal weights, from which the French Troy was derived, in [Chapter XVIII].