Symbol Parameter Name Unit  Definition Comments  Illustrations 
R_{a } average roughness µm  ${R}_{\text{a}}=\frac{1}{l}{\displaystyle {\int}_{0}^{l}\leftz\left(x\right)\right\text{d}x}$ 

It is the average surface roughness of the scanned profile around the mean line (the least squares mean line or that generated by a standard filter). It represents the average absolute deviation of the scanned profile points from a mean line.  
R_{q} root mean squared µm  ${R}_{\text{q}}=\sqrt{\frac{1}{l}{\displaystyle {\int}_{0}^{l}\left{z}^{2}\left(x\right)\right\text{d}x}}$ 

It is the root mean square deviation of a scanned profile on a mean line. This is a statistically meaningful parameter that is only recently gaining acceptance for industrial surface measurement but is widely used within the optical surface community. This value is typically 11% higher than R_{a}. It is further sensitive to peaks and valleys than R_{a} as the amplitudes are squared. Profile roughness (2D): R_{q}/R_{a} = 1.22 Profile roughness (3D): R_{q}/R_{a} = 1.25  
R_{sk} skewness  ${R}_{\text{sk}}=\frac{1}{{R}_{\text{q}}^{3}}\left[\frac{1}{l}{\displaystyle {\int}_{0}^{l}{z}^{3}\left(x\right)\text{d}x}\right]$ 

It is the roughness amplitude distribution and is a measure of the (a) symmetry processes produce nearGaussian distributions, with a skewness value close to 0.0. For asymmetric height distribution, the skewness can be negative or positive values. +ve for steep peaks and flat valleys. −ve for flat peaks and steep valleys.  
R_{ku} kurtosis  ${R}_{\text{ku}}=\frac{1}{{R}_{\text{q}}^{4}}\left[\frac{1}{l}{\displaystyle {\int}_{0}^{l}{z}^{4}\left(x\right)\text{d}x}\right]$ 

It is the roughness amplitude distribution and is a measure of the “peakedness” of the surface asperity heights about the profile mean line. A surface with a high kurtosis value tends to be peaky (large numbers of high asperities, and deep valleys) and produces a narrow asperity distribution. True Gaussian distribution has a kurtosis = 3  
R_{k} core roughness depth µm  The depth of the roughness core profile.  
R_{pk} reduced peak height µm  The average height of protruding peaks above roughness core profile.  
R_{vk} reduced valley depth µm  The average depth of valleys is projecting through roughness core profile.  
M_{r1} material portion 1 %  The level in %, determined for the intersection line which separates the protruding peaks from the roughness core profile. 