On the web page

you were asked to calculate an XBAR-S control chart. Here is the data for that problem.

```
Week01 1.097 1.204
Week03 1.030 1.362
Week05 0.682 0.978
Week07 0.820 1.080
Week09 1.042 0.858
Week11 1.398 1.146
Week13 1.301 1.204
```

Here are the summary statistics.

```
Mean Stdev
Week01 1.151 0.076
Week03 1.196 0.235
Week05 0.830 0.209
Week07 0.950 0.184
Week09 0.950 0.130
Week11 1.272 0.178
Week13 1.252 0.069`
```

The mean of the seven means is 1.09 and the mean of the seven standard deviations is 0.15. For subgroups of size 2, the constants are

```
A3=2.659, B3=0, B4=3.267.
```

The upper and lower control limits for the XBAR chart are

```
1.09+2.659*0.15=1.49 and
1.09-2.659*0.15=0.69.
```

The warning limits are

```
1.09+2.659*0.15*2/3=1.36 and
1.09-2.659*0.15*2/3=0.82.
```

Here is the control chart for the means (note that the numbers are slightly different because of rounding).

The upper control limit for the S chart is

```
3.267*0.15=0.49.
```

The distance from the center line to the upper control limit is

```
0.49-0.15=0.34.
```

The warning limit is placed at 2/3 of the distance from the center line or

```
0.15+0.34*2/3=0.38.
```

Here is the S chart (note again some slight discrepancies due to rounding).

You can find an earlier version of this page on my old website.