<Tr> <Td> Δ i (\ displaystyle \ Delta _ (i) \!) </Td> <Td> where delta i is calculated according to ASME B46. 1 and is a 5th order Savitzky--Golay smoothing filter </Td> <Td> Δ i = 1 60 d x (y i + 3 − 9 y i + 2 + 45 y i + 1 − 45 y i − 1 + 9 y i − 2 − y i − 3) (\ displaystyle \ Delta _ (i) = (\ frac (1) (60dx)) (y_ (i + 3) - 9y_ (i + 2) + 45y_ (i + 1) - 45y_ (i - 1) + 9y_ (i - 2) - y_ (i - 3))) </Td> </Tr> <P> Other "frequency" parameters are S, λ (\ displaystyle \ lambda) and λ (\ displaystyle \ lambda). S is the mean spacing between peaks . Just as with real mountains it is important to define a "peak". For S the surface must have dipped below the mean surface before rising again to a new peak . The average wavelength λ (\ displaystyle \ lambda) and the root mean square wavelength λ (\ displaystyle \ lambda) are derived from Δ (\ displaystyle \ Delta). When trying to understand a surface that depends on both amplitude and frequency it is not obvious which pair of metrics optimally describes the balance, so a statistical analysis of pairs of measurements can be performed (e.g.: R and λ (\ displaystyle \ lambda) or R and Sm) to find the strongest correlation . </P> <P> Common conversions: </P> <P> These parameters are based on the bearing ratio curve (also known as the Abbott - Firestone curve .) This includes the Rk family of parameters . </P>

What do mean by ra and rz values