Reconsider the data presented in Exercise 5.26.

a. Establish  x̅ and S control charts for compressive strength using these data. Is the process in statistical control? After establishing the control charts, 15 new subgroups were collected; the compressive strengths are shown in Table 5E.7. Plot the x̅ and S values against the previous control limits and draw conclusions.

b. Does the S chart detect the shift in process variability more quickly than the R chart did originally in part (b) of Exercise 5.26?