Question

15.3.6
The copper content of a plating bath is measured three times per day, and the results are reported in ppm. The x‾ and r values for 25 days are shown in the following table:

Day	x‾	r
1	5.45	1.21
2	5.39	0.95
3	6.85	1.43
4	6.74	1.29
5	5.83	1.35
6	7.22	0.88
7	6.39	0.92
8	6.50	1.13
9	7.15	1.25
10	5.92	1.05
11	6.45	0.98
12	5.38	1.36
13	6.03	0.83
14	7.01	1.45
15	5.83	1.37
16	6.35	1.04
17	6.05	0.83
18	7.11	1.35
19	7.32	1.09
20	5.90	1.22
21	5.50	0.98
22	6.32	1.21
23	6.55	0.76
24	5.90	1.20
25	5.95	1.19

Use the sampled data from problem #15.3.6 of the course textbook to construct a Stewhart ?"-chart. Assume the mean and standard deviation for ?" are 6.28 ppm and 0.39 ppm, respectively. Use the Western Electric Rules to determine if the process is in-control.

Answer 1