Page 202 - The Handbook for Quality Management a Complete Guide to Operational Excellence

188 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 189

52.5
UCL = 50.906

45.0

37.5
Defects PCL = 33.533

30.0

22.5

LCL = 16.161
15.0
1 4 7 10 13 16 19 22 25 28
Figure 9.15 c chart example constructed using Green Belt XL software
(courtesy of www.qualityamerica.com by permission).

Control Chart Selection
Selecting the proper control chart for a particular data set is a simple mat-
ter if approached properly as illustrated in Fig. 9.16.
To use the decision tree, begin at the left-most node and determine
whether the data are measurements or counts. If measurements, then
select the control chart based on the subgroup size. If the data are counts,

n
n
n

n np
n p

n c
n u

Figure 9.16 Decision tree for selecting control chart.

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