High Quality Content by WIKIPEDIA articles! In various manufacturing contexts (especially machining, fabricating, and additive manufacturing), an indicator is any of various instruments used to accurately measure small distances, and amplify them to make them more obvious. The name comes from the concept of indicating to the user that which their naked eye cannot discern; such as the presence, or exact quantity, of some small distance (for example, a small height difference between two flat surfaces, a slight lack of concentricity between two cylinders, or other small physical deviations).