A tube cutting process is producing tubes whose specification is 1030 millimeters long +/- 10 millimeters. Suppose that the process is off-centered from its target, with process mean (x-bar) equaling 1020 millimeters, and standard deviation 2 millimeters.

a) Find the process capability index using the appropriate formula. Is the process capable of meeting the specification for tube length?

(b) Why x-bar chart and R-chart are always used together? Discuss briefly.