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290 Part IV: Quality Assurance
Continued
Table 19.8
Number of nonconformities on printed boards for laptops per sample;
each sample consists of five inspection units.
Number of nonconformities
Number of nonconformities
Day per sample Day per sample
1 48 16 42
2 49 17 34
3 38 18 30
4 49 19 49
5 43 20 44
6 37 21 47
7 45 22 33
8 48 23 37
9 39 24 33
10 46 25 34
11 40 26 49
12 44 27 50
13 43 28 49
14 35 29 35
15 31 30 39
Part IV.B.4
Therefore,
u = c 41.
333
= = 8. 2667.
5 5
Hence, the control limits are given by
UCL = u+ 3 u/ n = 8. 2666+ 3 8. 2666/ 5 = 12.
124
CL = u = 826 . 67
LCL = u 3 u/ n = 8. 2666 3 8. 2666/ 5 = 4.
409
The u chart for the data in Table 19.8 is shown in Figure 19.14.
The u chart in Figure 19.14 shows that there are no assignable causes present in
the process. In other words, only common causes are affecting the process. Therefore,
management needs to take action on the system.
Continued