Nearly all measurement systems (old and new) are rooted in the measurements of the body, known as anthropometric measures. The cause is obvious – when a craftsperson needed to carry a measurement from one piece to another, or remember a length for later use, comparison to a body part was the most accessible means of doing so. There are a few exceptions I know of to this fact. For one, the origins of the meter lie in the decimal-obsessed attempt to arrive at a measure based on the Earth’s dimensions. Cartographers and mathematicians arrived at the meter, which was roughly one ten-millionth of the distance from the North Pole to the Equator, measured along the meridian that passed through Paris.
There are also systems that found their basis in abundant natural resources. As mentioned earlier, the length of three barleycorns, end to end, was used as a measure of the English inch for many centuries. In Japan, the kujirajaku or whale scale, was based on the length of a whale’s tooth, and is still used today by some traditional seamstresses. Whales have many teeth of very similar size, and barley corn is abundant in Europe – when you have a lot of a commodity that is roughly uniform in length, it is a good candidate for use as a base unit.
–Brendan Gaffney, excerpt from “Modern Revivalist Toolmaking: What Yesterday’s Tools Can Teach Us Today” in The First Three Issues