The identification of the surface texture used a number of parameters. These are different depending on the standard used and on the issue of the relevant standard. The notes below relate to the standards as listed above

R a - Average Roughness....
The average roughness is the area between the roughness profile and its mean line, or the integral of the absolute value of the roughness profile height over the evaluation length  Graphically, the average roughness is the area (shown below) between the roughness profile and its center line divided by the evaluation length normally five sample lengths with each sample length equal to one evaluation length. This is the parameter that has been used universally for many years. The European and ISO standard now more generally use R z:



Rt(R y), Rp, and R v ....
The peak roughness R< sub>p is the height of the highest peak in the roughness profile over the evaluation length Similarly, Rv is the depth of the deepest valley in the roughness profile over the evaluation length. The total roughness, R t(R y), is the sum of these two, or the vertical distance from the deepest valley to the highest peak.

R z....
R z is the sum of the height of the highest peak plus the lowest valley depth within a sampling length ( lr ).    R z is gnerally used, in European documents, to indicated the roughness surface texture   Note: The default evaluation length "ln" consists of 5 sample lengths "lr."