What is a dial indicator used for?

• A. To check runout.
• B. To measure roughness.
• C. To check runout, flatness, and other small variations in a workpiece or setup.
• D. To adjust feed rates.

Answer: (C)

A dial indicator is a precision tool for detecting tiny linear movements and deviations in a workpiece or setup. It amplifies small displacements into readable dial motion, so you can check how true or aligned things are. This includes runout on a rotating part, as well as flatness and other small variations across surfaces or setups. That broader capability—measuring runout, flatness, and similar tiny deviations—is why the best answer is the one that encompasses both runout and other small variations.

It isn’t used to measure surface roughness, which requires a roughness tester or profilometer, nor is it used to directly adjust feed rates, which is a machine control function rather than a measurement task.