I thought it was powers of two because it's not hard to find the halfway point between two other points, so you find the 1/2 mark, then the 1/4 mark, then 1/8, 16, 32, depending on how much precision you need. Then, at some point the unit changes again to mils or something like that.

After doing some digging in to this, I was thinking of the thou or mil, which is a thousandth of an inch. There's also another one that I hadn't heard of: the line, which is apparently equal to... 1/12 of an inch. Lol full circle.