Technician Development Program I Practice Exam

Ra is the average roughness. It represents the arithmetic mean of the absolute deviations of the surface profile from the mean line, measured over a specified length. This single number captures the overall roughness level of a surface and is the most commonly used parameter to describe texture. It isn’t a measure of maximum peaks or valleys (that would be other roughness metrics), nor does it describe material properties like hardness or friction. Keep in mind that Ra averages out details; two surfaces can have the same Ra but different peak/valley patterns, so additional parameters may be used if more detail is needed.