Process Capability. Process capability is the ability of a process to consistently meet specified customer-driven requirements Specification limits are set by management in response to customers’ expectations
Cpk = min(CPL, CPU)
Both Cp and Cpk are identical because process mean is at the center of the specification spread
As the process mean starts to drift away from the center of the specification spread, value of Cpk starts getting smaller (although Cp does not change)
You are the manager of a 500-room hotel. You have instituted a policy that all luggage deliveries must be completed within ten minutes or less. For seven days, you collect data on five deliveries per day. Compute an appropriate capability index for the delivery process.
Since there is only the upper specification limit, we need to only compute CPU. The capability index for the luggage delivery process is .8337, which is less than 1. The upper specification limit is less than 3 standard deviation above the mean.