Using CitectSCADA > Understanding Statistical Process Control > Control Chart Line Constants

Control Chart Line Constants

The table below shows the control chart line constants:

Samples in

Averages

Ranges

Standard Deviations

Group

A2

D2*

D3

D4

B3

B4

1

2.660

1.128

0

3.267

0

3.267

2

1.880

0

3.267

0

3.267

3

1.023

0

2.574

0

2.568

4

0.729

0

2.282

0

2.266

5

0.577

0

2.114

0

2.089

6

0.483

0

2.004

0.030

1.970

7

0.419

0.076

1.924

0.118

1.882

8

0.373

0.136

1.864

0.185

1.815

9

0.337

0.184

1.816

0.239

1.761

10

0.308

0.223

1.777

0.284

1.716

10

0.308

0.223

1.777

0.284

1.716

11

0.285

0.256

1.744

0.321

1.679

12

0.266

0.283

1.717

0.354

1.646

13

0.249

0.307

1.693

0.382

1.618

14

0.235

0.328

1.672

0.406

1.594

15

0.223

0.347

1.653

0.428

1.572

16

0.212

0.363

1.637

0.448

1.552

17

0.203

0.378

1.622

0.466

1.534

18

0.194

0.391

1.608

0.482

1.518

19

0.187

0.403

1.597

0.497

1.503

20

0.180

0.415

1.585

0.510

1.490

21

0.173

0.425

1.575

0.523

1.477

22

0.167

0.434

1.566

0.534

1.466

23

0.162

0.443

1.557

0.545

1.455

24

0.157

0.451

1.548

0.555

1.445

25

0.153

0.459

1.541

0.565

1.435

* D2 is only used for estimating standard deviation when there is one sample per subgroup.

Reference ANSI Z1.1-1985, Z1.2-1985 & Z1.3-1985: American National Standard, Guide for Quality Control Charts, Control Chart Method of Analyzing Data, Control Chart Method of Controlling Quality During Production.

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