A certain type of integrated circuit is connected to its frame by five wires. Thirty samples of five units each were taken, and the pull strength (in grams) of one wire on each unit was measured. The data are presented in Table E10 on page 787. The means are X̅ = 9.81, R̅ = 1.14, and s̅ = 0.4647.

a. Compute the 3σ limits for the R chart. Is the variance out of control at any point? If so, delete the samples that are out of control and recompute X̅ and R.

b. Compute the 3σ limits for the X̅ 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?