In various contexts of science, technology, and manufacturing (such as machining, fabricating, and additive manufacturing), an indicator is any of various instruments used to accurately measure small distances and angles, 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).
Many indicators have a dial display, in which a needle points to graduations in a circular array around the dial. Such indicators, of which there are several types, are often called dial indicators.
Other types of indicator include mechanical devices with cantilevered pointers and electronic devices with digital displays.
Indicators may be used to check the variation in tolerance during the inspection process of a machined part, measure the deflection of a beam or ring under laboratory conditions, as well as many other situations where a small measurement needs to be registered or indicated. Dial indicators typically measure ranges from 0.25 mm to 300 mm (0.015in to 12.0in), with graduations of 0.001 mm to 0.01 mm (metric) or 0.00005in to 0.001in (imperial/customary).
Various names are used for indicators of different types and purposes, including dial gauge, clock, probe indicator, pointer, test indicator, dial test indicator, drop indicator, plunger indicator, and others.