A dial gauge is a precision measurement commonly used to measure machined parts for production tolerances or wear. Dial gauges are capable of producing extremely fine measurement values; increments of 0.00005 inch (0.001mm) may be possible with some gauges. Measurement inputs are transferred to the gauge via a plunger, hinged lever, or the jaws of a vernier. Plunger instruments are generally used in conjunction with a clamp or stand which holds the gauge in a fixed position in relation to the workpiece. The workpiece is then rotated or moved to take the measurements. Dial gauges are available with analog needle and dial indicators or digital liquid crystal displays (LCDs).
The dial gauge has long been an standard with engineers, artisans, and do-it-yourself enthusiasts for taking very fine measurements on precision parts. High levels of accuracy are possible in extremely small increments with typical measurement ranges running from 0.015 inches to 12 inches (0.25 – 300 mm) in increments as small as 500 thousands of an inch (0.001 mm). There are two basic dial gauge formats; the first is the plunger or lever type gauge. In this case, a spring loaded plunger or lever at the bottom of the gauge transfers workpiece surface height deviations to the gauge. The second type is the vernier dial gauge which receives its measurement input from the movement of the jaws of a conventional vernier.
Plunger type dial gauges are typically held in a fixed position while taking measurements. Specially designed weighted or magnetic clamps or stands are used to support the instrument while the workpiece is rotated or moved. This process generally involves zeroing the gauge, adjusting its position until the plunger or lever rests on the workpiece, and then rotating or moving the work piece to check for anomalies. The contact tip of a lever type gauge is generally relatively small and measures narrow grooves where the plunger would not fit.
A vernier type dial gauge utilizes the movement of the verniers jaws as a measurement input. These gauges indicate measurements both on the dial and on the conventional vernier scale. The vernier type gauge is capable of producing very accurate measurements across the vernier's standard inside and outside diameter and depth measuring ranges. The analog dial gauge may be capable of allowing the needle to travel around the dial several times if the measurement input is large enough. These gauges then have a second, smaller dial, much like a wristwatch lap timer, on their face which indicate the number of full revolutions of the needle.
Digital indication dial gauges function in exactly the same way as their analog siblings but display their measurements digitally on a LCD display. Many users find this gauge quicker and easier to read than the needle and dial type. As with all precision instruments, care should be taken to keep the dial gauge clean and not subject it to excessive impact to preserve its accuracy.