Starrett SR200 Surface Roughness Tester - Manual (Page 6)

1.3 SR200 Specifications subject to change
Rmr: Material Ratio is the length of bearing surface (expressed as a percentage of the
evaluation length ln) at a depth below the highest peak.
Replaces tp% - Bearing Ratio as defined in ISO 4287 - 1984
RPc: Peak Count
The number of local peaks which project through a selectable band centred about the mean line
or a line parallel to it. The count is determined only over the evaluation length though the results
are given in peaks per cm (or per inch)
Known as Pc before 1997
Rsk: Skewness
Rsk is a measure of the symmetry of the profile about the mean line.
This parameter indicates whether the spikes on the surface are predominately negative or
positive or if the profile has an even distribution of peaks and valleys.
Rda: R Delta a or Rda or RDa - Arithmetical Mean Slope
Arithmetical Mean Slope of the Profile within the Sampling Length.