Why measure surface roughness?
Consider the history of a manufactured component. First there is the manufacture, next control by measurement and then the period of component’s use (performance). The intermediate step measurement is necessary because no manufacturing process remains constant and all production processes, including chemical and physical properties of the material, have to be monitored to detect changes, which could affect performance. Obviously the size and the shape of the component have to be correct, but the physical characteristics of the surfaces can be of equal importance — the hardness and the roughness for example.
