Lock Haven University describes the micrometer caliper as a metric instrument with a pair of jaws, one of which is movable, and a main scale calibrated to one-half millimeter. It has a thimble section consisting of a rotating handle with a circumference marked with 50 equal subdivisions. Zero the caliper, and position its jaws around the object to be measured. Then use the main and thimble scales in conjunction to check the precise measurement./
Make sure that fully closed jaws give a reading of zero on the Vernier micrometer caliper. If the instrument cannot be corrected using special wrenches to give a zero reading on full closure, you must add or subtract any error from the final reading when measuring an object.
Position the object between the caliper’s fixed and movable jaws. Lightly close down on the object using the instrument’s precise, uniform screw to close the movable jaw.
Read the measurement on the main scale and write it down. If the reading is not precise, use the lower reading as the main scale reading. Markings on the thimble scale are one-hundredth of a millimeter apart; divide the reading on the thimble by 100 to obtain the value to add to the main scale reading.