Repeat Exercise 12, using the S chart in place of the R chart.
In Exercise 12
a. Compute the 3σ limits for the  chart. Is the variance out of control at any point? If so, delete the samples that are out of control and recomputed  and .
b. Compute the 3σ limits for the  chart. On the basis of the 3σ limits, is the process mean in control? If not, at what point is it first detected to be out of control?
c. On the basis of the Western Electric rules, is the process mean in control? If not, when is it first detected to be out of control?