Test indicators, also called lever arm test indicators or dial test indicators, are precision mechanical tools used to accurately measure small linear distances, most commonly surface deviations. They measure the distance perpendicular to the surface of the object being tested by detecting the angular displacement of a hinged lever arm that touches the surface and converting it to a linear distance that can be read on the dial. The lever arm allows the tool to be held parallel to the surface instead of perpendicular, so that test indicators can take measurements in narrow grooves and small bores where a dial indicator cannot be used. The dial magnifies the measurement for readability, and has fine graduations for precise measurement. There are various types of test indicators that have different orientations of the dial face to match different applications. Test indicators are commonly used in manufacturing facilities, engineering workshops, and laboratories to set up and calibrate machines, determine lathe or mill runout and alignment, and check the tolerances of machined parts.
Lever arms are available in various lengths for different applications. The contact points (also called tips) are commonly ball shaped and made of any type of various materials that suit the measured surface and test environment. When selecting the appropriate test indicator, consider the material type and the measurement range, as required by the application.