In the Introduction to Metrology section we made reference to the development of the unit of length, the metre, and of the massive advances required by industry, especially because of International trade and the sub-contracting of manufacturing and assembly. Dimensional metrology has become critical to the success of these processes and continues to drive the uncertainties lower and lower.

The current standard for length is based on the speed of light. By using frequency stabilized lasers, a system of traceable length measurements has been developed. The instruments are known as laser interferometers. There are various grades of interferometers, with the highest being used in national research institutes, and many others down the accuracy scale. There are also three-dimensional machines known as coordinate measuring machines (CMMs).

However, the bulk of length and dimensional measurements are done using a vernier caliper and/or a micrometer. Laboratory-type vernier calipers incorporate a main scale and a sliding vernier scale which allow readings to the nearest 0.02 mm. This type of vernier can be used to measure outer dimensions of objects using the main jaws, and the inside dimensions using the smaller inverted jaws, and depth by using the stem.

The micrometer uses a screw gauge principle and is used to measure smaller dimensions than the vernier calipers. They also have two scales and are able to measure to a resolution of 0.001 mm. Both verniers and micrometers need special care when using them in high precision applications, as it is easy to make mistakes.

Verniers and micrometers are calibrated using gauge (sometimes referred to as gage) blocks and ring gauges, which, in turn, are calibrated by interferometers. There are many other instruments involved in dimensional metrology (analogue and digital) all working on basically the same systems but measuring other things, such as angle, screw threads etc.

Critical to dimensional metrology is an absolutely flat surface to work on, as close to zero vibration as possible and good temperature control. As usual, procedures play an important part, as it is easy for two metrologists to get two different results even when using the same equipment.

Instruments and artifacts required to be calibrated

The size of the laboratory will vary greatly, depending on the amount of work that it is required to do and how many workstations it has. It is likely to vary from 45 m2 up to 90 m2

Please refer to the Introduction to the metrology section for more information.