The test indicator is used to measure the small differences on a workpiece surface, to compare two different workpieces, or to compare a workpiece to another object of known dimensions, like a gauge block. The test indicator is one of the most common instruments used in inspection processes. Test indicators measure variations in heights, check for runout, and measure flatness. Test indicators can also be used to set tools, inspect the setup in a machine, or even measure the accuracy of the machine itself. Test indicators provide an advantage over dial indicators because they can be used to measure in smaller spaces.
Test indicators are often categorized by either the movement of one of its components, or by the position of its dial in relation to its other part. The indicator selected is usually based on the one that can be positioned to measure the workpiece and be read easily.