Mitutoyo SJ-301 - Definitions of the SJ-301 Roughness Parameters

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14.5 Definitions of the SJ-301 Roughness Parameters
This section gives the definitions (calculation methods) of the roughness parameters that can
be measured with the SJ-301.
Sampling length ᐉ
Evaluation length ᐉn = n x ᐉ
Sampling length and evaluation length
Each parameter explained below is defined as calculated within a sampling length. Specific
parameters to be obtained over the evaluation length will be noted as required.
14.5.1 Arithmetic mean deviation of the profile, Ra
Ra is the arithmetic mean of the absolute values of the profile deviations (Yi) from the mean
line.
N
i=1
Ra =
1
N
Yi
∑
● For ANSI, Ra is defined over the entire evaluation length.
14.5.2 Root-mean-square deviation of the profile, Rq
Rq is the square root of the arithmetic mean of the squares of profile deviations (Yi) from the
mean line.
N
i=1
Rq = ( )
1
N
1
2
Yi
∑
2
Yi
● For ANSI, Rq is defined over the entire evaluation length.