Prevent the jaws from creeping forward or backward as you measure. They move only when you press a button, then lock in place when you let go. The button falls naturally under your thumb, so you can operate these calipers comfortably with one hand.

These classic calipers use a sliding vernier scale. Just add the measurement from the main scale to the measurement on the vernier scale to get accurate readings as small as 0.001". Made completely out of metal, they won't break when dropped or short-circuit when wet. They're battery-free, so they're always ready to use.