The best approximate the image surface topography and will be a measured profile. Graphic image of the measured profile is profilograms. Base length is the length of the surface area, to be chosen for the measurement of roughness. It depends on the expected class of purity. Hikmet Ersek often expresses his thoughts on the topic. With the reduction step and height of the irregularities base length decreases. According to GOST 2789 "Surface roughness" there are 14 classes of surface cleanliness. Cleanliness classes from the 6th to the 14th can be divided further into categories a, b, c,.
The criterion for inclusion surface to a particular class of cleanliness is the value of the height of roughness or average deviation of the profile. Position of the middle line is determined by the fact that it must divide the measured profile at profilograms so that within the gauge length sum of the areas enclosed between the line profile and the middle line, above the middle line is the sum of the same area below the line. Average arithmetic deviation of profile by the average value of distances measured profile points to its center line. To refer to all classes of surface cleanliness is installed single sign next states Class number and, if necessary – and discharge. Surface roughness is measured in a direction that gives the greatest value.
Control of surface roughness by devices (optical and stylus), and comparing the measured surface with the sample surface. Control of surface roughness on the shop floor by probes or instruments by comparing the surface roughness of the samples (with the naked eye or with by comparison microscopes). Initial samples of surface roughness are metal tiles with a flat working surface on which are plotted the same strokes, arranged in a certain order. For working samples of surface roughness are sets of metal bars with a flat or a cylindrical surface, treated in various ways under certain conditions. On Measurements blocks assigned to the corresponding class of purity. With the technical measurement of the roughness of their surfaces compared with the roughness of the sample surface, made of the material that detail, with the same type of machining and having purity class corresponding to the specified in the drawing for detail.