Dial test indicators generally resemble the more general-purpose dial indicators, but have different internal construction (note that the hard-tipped contact lever moves crosswise, not up-and-down), and are generally used in different applications. The range is more limited than that of a dial indicator, but the instrument is generally more compact. Balanced dials are near universal.
Similar to a plunger-like dial indicator, a test indicator uses a train of gear to amplify movement of the contact point. The sideways motion of the contact lever, however, means the input to this gear train comes from a sector gear arrangement rather than the rack and pinion of a plunger-type instrument.
A test indicator has an advantage over a plunger-type dial indicator in situations in which a linear plunger would need a bell-crank linkage of some sort to â€œreach intoâ€?the work. The usually smaller overall size also helps.