Suppose you had an X-bar chart and an R-chart for some quali…
Suppose you had an X-bar chart and an R-chart for some quality aspect, as follows. The center line for the X-bar chart was 20, the upper control limit was 21.8, and the lower control limit was 18.2. The center line for the R-chart was 2. The sample size is 7. A quick and dirty estimate of the natural tolerances would be