Page 198 - The Handbook for Quality Management a Complete Guide to Operational Excellence

184 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 185

These values are shown in the last column of Table 9.9.
sum of subgroup count of occurrences 1544
u = = = 48.25
sum of subgroup unit sizes 32
f
which is constant for all subgroups.
n = 1 unit:

.
u 48 25
LCL = u − 3 = 48 25 3 = 27 411
−
.
.
n 1
.
u 48 25
UCL = u + 3 = 48.225 3+ = 69 089
.
n 1
n = 2 units:
48 25
.
−
.
LCL = 48 25 3 = 33 514
.
2
.
48 25
+
.
2
UCL = 48 25 3 = 62 986
.
2
The control limits and the subgroup occurrences-per-unit are shown
in Fig. 9.14.
70
UCL = 62.985

55
Defects per unit PCL = 48.250

40

LCL = 33.515

25
1 3 5 7 9 11 13 15 17 19 21 23 25
Figure 9.14 u chart example constructed using Green Belt XL software
(Courtesy of www.qualityamerica.com by permission).

09_Pyzdek_Ch09_p151-208.indd 185 11/21/12 1:42 AM