Dial test indicator

A Dial test indicator, also known as a lever arm test indicator or finger indicator, has a smaller measuring range than a dial indicator and therefore has the ability to measure in smaller increments. A test indicator measures the deflection of the arm, the probe does not retract but swings in an arc around its hinge point. The lever may be interchanged for length or ball diameter and permits measurements to be taken in narrow grooves and small bores where the body of a probe type may not reach. The model shown is bidirectional, some types may have to be switched via a side lever to be able to measure in the opposite direction.

These indicators actually measure angular displacement and not linear displacement. If a force is perpendicular to the finger, the linear displacement error is acceptably small within the display range of the dial. However, this error starts to become noticeable when the force is as much as 10 degrees off the ideal 90. These indicators are used to compare two surfaces and alert the user when they are at the same position relative to the body of the indicator. In this application the force can be applied at almost any angle since you are looking for the same reading on two different surfaces.


Digital indicator
With the advent of electronics and LCDs the clock face and analog display has been replaced with digital displays, these have the added advantage of sometimes being able to record and transmit the data electronically to a computer. This process is known as statistical process control (SPC) and involves a computer recording and interpreting the results, this also reduces the risk of the operator introducing recording errors. Digital indicators can also be switched between imperial and metric units with the press of a button, thereby increasing the DTI's versatility.