Cp

The first of the capability indices we will look at is Cp.

Cp is a long-term or on-going measure of the potential of a process relative to specification. This index is calculated from data gathered over a considerable time frame to ensure that all common causes of variation are included.

It is important to remember that Cp is a measure of process potential. Process potential is an estimate of the process' ability to consistently deliver output within the customer's specified tolerance, assuming that the process remains in a state of statistical control and assuming that the process mean is equal to the nominal value.