Definition

A measure of process performance which takes into account the centering of the process. P_{pk} is calculated by dividing the distance of the process mean to the nearest specification, by 3 times the process standard deviation. If the process is centered exactly in the middle of the tolerance range, P_{pk} is equal to P_{p}.

Examples

The formula to calculate P_{pk} is shown, where USL and LSL are the upper and lower specification limits respectively and the process standard deviation 's_{calculated}' is obtained directly from the data.

Consider this example:

The Lower Specification Limit is 48

The Upper Specification Limit is 60

The process mean is 57

The calculated standard deviation is 1.65, giving a 3-Sigma process spread of 3*1.65 = 4.95.

Therefore, P_{pk} is is the minimum of: (57-48)/4.95 = 1.82 and (60-57)/4.95 = 0.61.

So P_{pk} is 0.61.

See Also

P_{p},
C_{p},
C_{pk}