Applied Statistics and Probability for Engineers

634 CHAPTER 16 STATISTICAL QUALITY CONTROL

indicated. Thus, the V mask forms a visual frame of reference similar to the control limits on

an ordinary Shewhart control chart. For the technical details of designing the V mask, see

Montgomery (2001).

While some computer programs plot CUSUMS with the V-mask control scheme,

we feel that the other approach to CUSUM control, the tabular CUSUM,is superior.

Table 16-7 CUSUM Computations for the Chemical Process Concentration Data in Table 16-3

Observation,ixi xi 99 si(xi99)si 1

1 102.0 3.0 3.0

2 94.8 4.2 1.2

3 98.3 0.7 1.9

4 98.4 0.6 2.5

5 102.0 3.0 0.5

6 98.5 0.5 0.0

7 99.0 0.0 0.0

8 97.7 1.3 1.3

9 100.0 1.0 0.3

10 98.1 0.9 1.2

11 101.3 2.3 1.1

12 98.7 0.3 0.8

13 101.1 2.1 2.9

14 98.4 0.6 2.3

15 97.0 2.0 0.3

16 96.7 2.3 2.0

17 100.3 1.3 0.7

18 101.4 2.4 1.7

19 97.2 1.8 0.1

20 101.0 2.0 1.9

1 234567891011121314151617181920

Observation, i

–2

+4

–4

0

+2

si

Figure 16-19 Plot of

the cumulative sum for

the concentration data,

Table 16-7.

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