Actually, “ounce” means “one twelfth”. (So does “inch”.) That’s why a Troy pound is made up of twelve Troy (for a city in France) ounces. But a good set of Troy weights was expensive, and dividing by twelve was hard, so a new, sloppy kind of weights came into being, with cheap scales, and with sixteen ounces to the pound, so you could just divide over and over again by two. The crappy new avoirdupois weights took over, except for measuring gold and jewelry, where precision was more important and Troy weight continued in use, and also except for measuring drugs, where a third system, apothecary’s weight (based on Troy weight) was used.
Of course, it also mattered what city you were in. Troy pounds were the same everywhere, but avoirdupois weights were wobbly. It was only in 1826 that the British Empire settled on one avoirdupois pound, and the USA and the British Empire didn’t agree on how much a pound was until 1959.
Actually, “ounce” means “one twelfth”. (So does “inch”.) That’s why a Troy pound is made up of twelve Troy (for a city in France) ounces. But a good set of Troy weights was expensive, and dividing by twelve was hard, so a new, sloppy kind of weights came into being, with cheap scales, and with sixteen ounces to the pound, so you could just divide over and over again by two. The crappy new avoirdupois weights took over, except for measuring gold and jewelry, where precision was more important and Troy weight continued in use, and also except for measuring drugs, where a third system, apothecary’s weight (based on Troy weight) was used.
Of course, it also mattered what city you were in. Troy pounds were the same everywhere, but avoirdupois weights were wobbly. It was only in 1826 that the British Empire settled on one avoirdupois pound, and the USA and the British Empire didn’t agree on how much a pound was until 1959.