A standard caliper can be used to measure a number of different objects, using internal placement, external placement, and depth. Specifically, a caliper has a tool at the narrow end of it called a depth rod. The depth rod on a caliper extends out from the caliper. The depth of a particular object can be measured by putting the depth rod into the hole you are getting a measurement of. You can have the depth rod extend more or less further from the caliper using the jaws on the side. Move the thumb screw carefully so that the end of the beam scale is resting at the top of the hole. Then, adjust the depth rod so that it is hitting the bottom of the hole and pressing against the interior wall of the hole. Turn the lock screw in order to tighten the jaws. This allows you to be able to remove the hole and object you are measuring and just read the caliper. Finally, read your caliper and see an accurate read out of the depth of the hole.