Mitutoyo SURFTEST SJ-410 - Definitions of the SJ-410 Roughness Parameters; Ra (JIS1994, JIS2001, ISO1997, ANSI, VDA, Free): Arithmetic Mean of Roughness, Ra (JIS1982): Arithmetic Mean Deviation of Roughness; Rq (JIS2001, ISO1997, ANSI, VDA, Free): Mean Square of Roughness

No. 99MBB765A
23-18
23.5 Definitions of the SJ-410 Roughness Parameters
This section explains the definitions (calculation methods) of the roughness parameters
that can be measured with the SJ-410.
Sampling length and evaluation length
The following explanations show the how the parameters are calculated based on the
sampling length. Parameters that are calculated based on the evaluation length are noted
as such.
23.5.1 Ra (JIS1994, JIS2001, ISO1997, ANSI, VDA, Free): Arithmetic mean of roughness,
Ra (JIS1982): Arithmetic mean deviation of roughness
Ra is the arithmetic mean of the absolute values of the evaluation profile deviations (Yi)
from the mean line.
∑
=
=
n
i
iY
n
Ra
1
1
• For ANSI, Ra is defined over the entire evaluation length.
23.5.2 Rq (JIS2001, ISO1997, ANSI, VDA, Free): Mean square of roughness
Rq is the square root of the arithmetic mean of the squares of the deviations (Yi) from the
mean line to the evaluation profile.
2
1
1
2
1






=
∑
=
n
i
Yi
n
Rq
• For ANSI, Rq is defined over the entire evaluation length.
Sampling length ℓ
Evaluation length ℓn = ℓ × n