The height of objects and the depth of holes, slots etc, are measured by the height gauge and depth gauge respectively. A dial gauge is often used in conjunction with these instruments to improve measurement accuracy. The height gauge effectively consists of a vernier caliper mounted on a flat base. Measurement inaccuracy levels down to ┬▒0.015% are possible. The depth gauge is a further variation on the standard vernier caliper principle that has the same measurement accuracy capabilities as the height gauge.
In practice, certain difficulties can arise in the use of these instruments where either the base of the instrument is not properly located on the measuring table or where the point of contact between the moving anvil and the workpiece is unclear. In such cases, a dial gauge, which has a clearly defined point of contact with the measured object, is used in conjunction with the height or depth gauge to avoid these possible sources of error. These instruments can also be obtained in intelligent versions that give a digital display and have self-calibration capabilities.
The dial gauge consists of a spring-loaded probe that drives a pointer around a circular scale via rack and pinion gearing. Typical measurement resolution is 0.01mm. When used to measure the height of objects, it is clamped in a retort stand and a measurement taken of the height of the unknown component. Then it is put in contact with a height gauge that is adjusted until the reading on the dial gauge is the same.