Calculating Control Limits

GainSeeker calculates control limits in several user-definable methods. You can calculate control limits for Range and charts using the Factors or Sample Standard Deviation (SSD) methods. When the subgroup size is one, the calculations are slightly different.

Factors method of calculating control limits for Range charts:

Sample Standard Deviation method of calculating control limits:

Factors method of calculating control limits for S charts:

Short Run limits:

Non-symmetrical control limits:

Assumptions when calculating control limits:

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Subgroup size

A2

A3

B3

B4

E2

D3

D4

2

1.880

2.659

-----

3.267

2.66 

-----

3.267

3

1.023

1.954

-----

2.568

1.772

-----

2.574

4

0.729

1.628

-----

2.266

1.457

-----

2.282

5

0.577

1.427

-----

2.089

1.290

-----

2.114 

6

0.483

1.287

0.030

1.970 

1.184

-----

2.004

7

0.419

1.182

0.118

1.882

1.109

0.076

1.924

8

0.373

1.099

0.185

1.815

1.054 

0.136

1.864

References: