Mitutoyo SURFTEST SJ-410 - Ppi (Free): Peak Count; Δa (ANSI, Free): Slope of the Arithmetic Mean (Angle of the Mean Slope); Rδq (ISO1997, JIS2001, ANSI, VDA, Free): Mean Square Slope (Angle of the Mean Square Slope); Λa (Free): Arithmetic Mean of Wavelength

No. 99MBB765A
23-28
23.5.17 Ppi (Free): Peak count
Ppi is the value obtained by calculating the number of peaks that occur in 25.4 mm (1.00
in) of Pc.
TIP
• The unit for Ppi is displayed as /E (E = 25.4 mm (1.00 in)).
23.5.18 Δa (ANSI, Free): Slope of the arithmetic mean (angle of the mean slope)
Δa is the arithmetic mean of the absolute values of the local slopes (dz/dx) of the
evaluation profile. The local slope (dz/dx) of the evaluation profile is given by the following
formula:
∑
=
=∆
n
i
dx
dzi
n
a
1
1
(
)
32112
3
945459
60
1
−−−++
+
−+−+−
∆
=
iiii
ii
zzzzzz
xdx
dzi
Zi is the height of the i’th point, and Δx is the distance to the adjacent data point.
• For ANSI, RΔa is defined over the entire evaluation length.
23.5.19 RΔq (ISO1997, JIS2001, ANSI, VDA, Free): Mean square slope (angle of the
mean square slope)
Δq is the square root of the arithmetic mean of the squares of the local slope (dz/dx) of the
evaluation profile.
2
1
1
∑
=






=∆
n
i
dX
dZi
n
qR
• For ANSI, RΔq is defined over the entire evaluation length.
23.5.20 λa (Free): Arithmetic mean of wavelength
λa is the mean wavelength estimated from Δa that can be obtained from the formula
below.
a
Ra
a
∆
×=
360 λ
23.5.21 λa (Free): Mean square slope
λq is the mean wavelength estimated from Δq that can be obtained from the formula
below.
q
Rq
q
∆
×= 360
λ
23.5.22 Lo (Free): Developed profile length
When an evaluation profile has developed into a line without profile irregularities, the line
length Lo is given by the following formula.
( )
∑
=
∆+∆=
n
I
XYiLo
1
2
1
22