Surface roughness is a measurement of surface texture. It is defined as a vertical deviation of a real surface from its ideally smooth form. Roughness plays an important role in various processes such as friction and adhesion and is widely measured
Depending on the size of these deviations the surface will either be rough or smooth. A very rough surface will interact differently with other materials due to the coefficient of friction. This may be undesirable when a contact between two parts must be smooth. However, manufacturing a very fine surface is costlier. The application of the parts and their interactions to surface condition will ultimately determine the desirable surface roughness.
The profilometer is a tool designed to measure the deviations in surface texture. A diamond tipped stylus runs over the surface of the material reacting with variations in surface texture. When a variation is measured high or low, the profilometer reports the variant data. After scanning, the surface will be given a rating in roughness per the specification requested.