Compute the 3𝜎 \overline{X} chart upper and lower control limits for the moisture data in Table 10.1.
TABLE 10.1 Moisture content for salt packages, as a percentage of total weight | ||||||||
Sample | Sample Values | Mean (\overline{X}) | Range (R) | SD (s) | ||||
1 | 2.53 | 2.66 | 1.88 | 2.21 | 2.26 | 2.308 | 0.780 | 0.303 |
2 | 2.69 | 2.38 | 2.34 | 2.47 | 2.61 | 2.498 | 0.350 | 0.149 |
3 | 2.67 | 2.23 | 2.1 | 2.43 | 2.54 | 2.394 | 0.570 | 0.230 |
4 | 2.10 | 2.26 | 2.51 | 2.58 | 2.28 | 2.346 | 0.480 | 0.196 |
5 | 2.64 | 2.42 | 2.56 | 2.51 | 2.36 | 2.498 | 0.280 | 0.111 |
6 | 2.64 | 1.63 | 2.95 | 2.12 | 2.67 | 2.402 | 1.320 | 0.525 |
7 | 2.58 | 2.69 | 3.01 | 3.01 | 2.23 | 2.704 | 0.78 | 0.327 |
8 | 2.31 | 2.39 | 2.60 | 2.40 | 2.46 | 2.432 | 0.290 | 0.108 |
9 | 3.03 | 2.68 | 2.27 | 2.54 | 2.63 | 2.63 | 0.760 | 0.274 |
10 | 2.86 | 3.22 | 2.72 | 3.09 | 2.48 | 2.874 | 0.740 | 0.294 |
11 | 2.71 | 2.80 | 3.09 | 2.60 | 3.39 | 2.918 | 0.790 | 0.320 |
12 | 2.95 | 3.54 | 2.59 | 3.31 | 2.87 | 3.052 | 0.950 | 0.375 |
13 | 3.14 | 2.84 | 3.77 | 2.80 | 3.22 | 3.154 | 0.970 | 0.390 |
14 | 2.85 | 3.29 | 3.25 | 3.35 | 3.59 | 3.266 | 0.740 | 0.267 |
15 | 2.82 | 3.71 | 3.36 | 2.95 | 3.37 | 3.242 | 0.890 | 0.358 |
16 | 3.17 | 3.07 | 3.14 | 3.63 | 3.70 | 3.342 | 0.630 | 0.298 |
17 | 2.81 | 3.21 | 2.95 | 3.04 | 2.85 | 2.972 | 0.400 | 0.160 |
18 | 2.99 | 2.65 | 2.79 | 2.80 | 2.95 | 2.836 | 0.340 | 0.137 |
19 | 3.11 | 2.74 | 2.59 | 3.01 | 3.03 | 2.896 | 0.520 | 0.221 |
20 | 2.83 | 2.74 | 3.03 | 2.68 | 2.49 | 2.754 | 0.540 | 0.198 |
21 | 2.76 | 2.85 | 2.59 | 2.23 | 2.87 | 2.66 | 0.640 | 0.265 |
22 | 2.54 | 2.63 | 2.32 | 2.48 | 2.93 | 2.58 | 0.610 | 0.226 |
23 | 2.27 | 2.54 | 2.82 | 2.11 | 2.69 | 2.486 | 0.710 | 0.293 |
24 | 2.40 | 2.62 | 2.84 | 2.50 | 2.51 | 2.574 | 0.440 | 0.168 |
25 | 2.41 | 2.72 | 2.29 | 2.35 | 2.63 | 2.48 | 0.430 | 0.186 |
26 | 2.40 | 2.33 | 2.40 | 2.02 | 2.43 | 2.316 | 0.410 | 0.169 |
27 | 2.56 | 2.47 | 2.11 | 2.43 | 2.85 | 2.484 | 0.740 | 0.266 |
28 | 2.21 | 2.61 | 2.59 | 2.24 | 2.34 | 2.398 | 0.400 | 0.191 |
29 | 2.56 | 2.26 | 1.95 | 2.26 | 2.40 | 2.286 | 0.610 | 0.225 |
30 | 2.42 | 2.37 | 2.13 | 2.09 | 2.41 | 2.284 | 0.330 | 0.161 |
31 | 2.62 | 2.11 | 2.47 | 2.27 | 2.49 | 2.392 | 0.510 | 0.201 |
32 | 2.21 | 2.15 | 2.18 | 2.59 | 2.61 | 2.348 | 0.460 | 0.231 |
\overline{\overline{X}}= 2.6502 | \overline{R} = 0.6066 | \overline{s} = 0.2445 |
With sample 6 deleted, the value of \overset{=}{ X} is 2.658, and the value of \overline{R} is 0.5836. The sample size is n = 5. From the table, A_{2} = 0.577. Therefore the upper control limit is 2.658 + (0.577)(0.5836) = 2.995, and the lower control limit is 2.658−(0.577)(0.5836) = 2.321.