Doctors measure with spider legs

Saw doctors use spiders to measure the amount of set in each tooth.

Supporting the spider on 4 fingers, I offer it up to the tooth-tip. If that spider won’t rock in any direction, the tooth is set to that spider and I can then move along 2 teeth to measure the set of next tooth.

If the spider rocks on its long axis, I place an anvil below the tooth-tip and strike from above with a hammer. If spider rocks on its short axis the tooth is over-set.

The following videos should help to illustrate.

From above…

And from below…