Avoirdupois

This year's Mothers' Union diary has a word that I've never come across. I though that pounds and ounces were the Imperial system. It appears that there is a much older system called Avoirdupois which was then adopted into law in Britain in the 1800s. I was interested to read that the pound was divided into 16 ounces because 16 divides evenly by 2 several times. I suppose the systems were devised by merchants originally and are based on practical considerations rather than mathematical logic. Try https://en.wikipedia.org/wiki/Avoirdupois_system and https://en.wikipedia.org/wiki/Imperial_units