Until recently I had never heard the size-of-a-stick, wife-beating, stick size definition of rule-of-thumb and assumed immediately that it was an urban legend.

I had always been taught that it meant measuring with the tip of your tumb - which is roughly one inch long. An experienced woodworker who always uses this same measure would have been accurate enough. It is like somebody who measure distance with his paces. If you know you pace at three feet then you can be accurate enough.