TABLE 18-7 A Supplier of Silicone Sheets for Producers of Computer Chips

TABLE 18-7
A supplier of silicone sheets for producers of computer chips wants to evaluate her manufacturing process.She takes sample sizes of 5 from each day's output and counts the number of blemishes on each silicone sheet.The results from 20 days of such evaluations are presented below.
Sheet
Day 1 2 3 4 5 Mean Range
1 8 10 14 6 5 8.6 9
2 8 13 6 6 10 8.6 7
3 10 12 7 7 9 9.0 5
4 5 9 12 7 10 8.6 7
5 8 3 8 9 10 7.6 7
6 9 7 9 6 9 8.0 3
7 10 10 5 7 6 7.6 5
8 10 9 10 6 5 8.0 5
9 6 10 6 9 9 8.0 4
10 6 9 8 6 8 7.4 3
11 8 5 6 10 10 7.8 5
12 6 4 7 7 12 7.2 8
13 7 5 7 6 9 6.8 4
14 5 8 8 7 6 6.8 3
15 7 12 10 6 10 9.0 6
16 7 11 4 7 8 7.4 7
17 8 4 5 4 7 5.6 4
18 11 4 11 11 10 9.4 7
19 6 10 6 10 10 8.4 4
20 6 12 12 6 8 8.8 6
She also decides that the upper specification limit is 10 blemishes.
-Referring to Table 18-7,an R chart is to be constructed for the number of blemishes.One way to create the upper control limit involves multiplying the mean of the sample ranges by D₄.For this data set,the value of D₄ is ________.