Factors for Computing Control Chart Limits for X and R Charts

Sample Size (n)

Mean Factor (A2)

Upper Range (D4)

Lower Range (D3)

2

1.880

3.268

0

3

1.023

2.574

0

4

0.729

2.282

0

5

0.577

2.115

0

6

0.483

2.004

0

7

0.419

1.924

0.076

8

0.373

1.864

0.136

9

0.337

1.816

0.184

10

0.308

1.777

0.223