Precision reference specimen

Precision reference specimens
Precise measurements of surface roughness can be made only by means of a measuring instrument in which a pickup traces over the surface and analyses the resulting data. Many different types are available, ranging from inexpensive workshop roughness testers to sophisticated computerised laboratory systems; and making use of different technologies for the pickup, such as atomic force probes or laser beams, as well as the more widely-used contacting diamond stylus method.
All these roughness measuring instruments have to be checked and calibrated against standard surfaces with accurately known features. For example, the overall vertical magnification of the system is checked by measuring a surface which has a step with accurately-known height, or a groove or valley with accurately-known depth.
Other specimens will be necessary (depending upon the type of instrument) for checking the roughness parameter readings, filters, stylus tip size and condition, horizontal magnification, and linearity. Such specimens are called precision reference standards or specimens.