4.12 Roughness Average (RA)-The arithmetic average of the absolute values of the measured profile height deviations taken within the roughness sampling length and measured from the graphical centerline. For electrical averaging instruments, the term cutoff is used to represent the roughness sampling length. Roughness average is specified in micrometers or microinches. Roughness average is also known as arithmetical average (AA) and centerline average (CLA). Older instruments calibrated to display "RMS" values will give values 11% higher than roughness average (RA).