ppk - Assessing Overall Performance without Targets
When no target is given, ppk is used as the primary performance measure in place of ppm. ppk may be calculated as follows.
where
- USL is the Upper Specification Limit,
- LSL is the Lower Specification Limit,
- s is the sample standard deviation from all combined data, and
is the sample mean from all combined data.
ppk is maximized by minimizing variation and increasing the distance from the nearest specification.