Atlas Copco PowerMACS 4000

SPC and Statistics
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7.2.4 SPC constants
The table below gives the constants to use in the mathematical formulas.
Sub-
group
size
Divisors for
estimate of
standard dev.
Factors for Control Limits
n
d2
c4
A2
D3
D4
A3
B3
B4
2
1.13
0.798
1.88
-
3.27
2.66
-
3.27
3
1.69
0.886
1.02
-
2.57
1.95
-
2.57
4
2.06
0.921
0.73
-
2.28
1.63
-
2.27
5
2.33
0.940
0.58
-
2.11
1.43
-
2.09
6
2.53
0.952
0.48
-
2.00
1.29
0.03
1.97
7
2.70
0.959
0.42
0.08
1.92
1.18
0.12
1.88
8
2.85
0.965
0.37
0.14
1.86
1.10
0.19
1.82
9
2.97
0.969
0.34
0.18
1.82
1.03
0.24
1.76
10
3.08
0.973
0.31
0.22
1.78
0.98
0.28
1.72
11
3.17
0.975
0.29
0.26
1.74
0.93
0.32
1.68
12
3.26
0.978
0.27
0.28
1.72
0.89
0.35
1.65
13
3.34
0.979
0.25
0.31
1.69
0.85
0.38
1.62
14
3.41
0.981
0.24
0.33
1.67
0.82
0.41
1.59
15
3.47
0.982
0.22
0.35
1.65
0.79
0.43
1.57
16
3.53
0.984
0.21
0.36
1.63
0.76
0.45
1.55
17
3.59
0.985
0.20
0.38
1.62
0.74
0.47
1.53
18
3.64
0.985
0.19
0.39
1.61
0.72
0.48
1.52
19
3.69
0.986
0.19
0.40
1.60
0.69
0.50
1.50
20
3.74
0.987
0.18
0.42
1.59
0.68
0.51
1.49
21
3.78
0.988
0.17
0.42
1.58
0.66
0.52
1.48
22
3.82
0.988
0.17
0.43
1.57
0.65
0.53
1.47
23
3.86
0.989
0.16
0.44
1.56
0.63
0.55
1.46
24
3.90
0.989
0.16
0.45
1.55
0.62
0.56
1.45
25
3.93
0.990
0.15
0.46
1.54
0.61
0.57
1.44