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182 P r o c e s s C o n t r o l Q u a n t i f y i n g P r o c e s s Va r i a t i o n 183

Shipment Number Bruised Peaches
1 20
2 28
3 24
4 21
5 32
6 33
7 31
8 29
9 30
10 34
11 32
12 24
13 29
14 27
15 37
16 23
17 27
18 28
19 31
20 27
21 30
22 23
23 23
24 27
25 35
26 29
27 23
28 23
29 30
30 28
TOTAL 838

Table 9.8 Raw Data for np Chart
of events. For example, when using a p chart one would count bruised
peaches. When using a u chart one would count the bruises.
Control Limit Equations for u Charts Like all control charts, u charts consist of
three guidelines: centerline, a lower control limit, and an upper control
limit. The centerline is the average number of occurrences-per-unit and

09_Pyzdek_Ch09_p151-208.indd 182 11/21/12 1:42 AM