Here's one for our luthiers... I'm wondering what kind of a tool is usually used to measure the thickness of things like tops, backs and ribs. I know there are special large calipers made specifically for this, but they're quite expensive and I'm sure makers hundreds of years ago didn't have such things. I haven't been able to think of anything else that would work, except calipers like are used in turning bowls. That doesn't seem like it would be very accurate, at least for something as precise as a musical instrument... So what are people using?