An internal quality control sample of blood, used for checking the accuracy of blood alcohol determinations, contains 80.0 mg 100 ml−1 of ethanol. Successive daily measurements of the alcohol level in the sample were made using four replicates. The precision (process capability) of the method was known to be 0.6 mg 100 ml−1. The following results were obtained:

Day	Concentration (mg 100 ml−1)
1	79.8
2	80.2
3	79.4
4	80.3
5	80.4
6	80.1
7	80.4
8	80.2
9	80.0
10	79.9
11	79.7
12	79.6
13	79.5
14	79.3
15	79.2
16	79.3
17	79.0
18	79.1
19	79.3
20	79.1

Plot the Shewhart chart for the mean, and the CUSUM chart, for these results, and comment on the outcomes.