I read once that sheet metal gauges started out as the number of sheets stacked together to make a pile 1" thick. I'm not sure that's true anymore but it might not be too far off.
Shotgun gauges were how many lead balls that would fit the barrel and equal a pound, except for the .410 which is the actual diameter in inches.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.