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waht exactly is diff b/w PPk & CPk for Sigma Multiple calculation.
Ppk doesn’t require a process to be in statiscal control, while Cpk does.Ppk can be calculated by using direct calculations of mean and variations from a group of observations, say 40 measurements. Then you use USL, LSL, mean & variation to get Ppk.Cpk is calculated after the Control charts have been constructed and the process is shown in control. And you use the formula of constructing control charts to calculate the mean, variation. Then the Cpk can be calculated.In short, Cpk means a process is in statistical control and its capability as indicated. Ppk not requires in statistical control.Ppk is not useful but creats confusions.
wow…really wrong…The calculations are identical, with Ppk simply using a long term view of the variation in the process, usually indicating less capability (ie a smaller value than Cpk).
It is said to better approximate how your customer experiences the quality of your process.
A typical capability analysis would run both the C and the P calculations to gain a greater understanding of the current process´s potential – and actual – ability to meet customer specs in both the short and long term.
“The calculation are identical, but Ppk usually smaller than Cpk.”
Is it right to conclude that Cpk explains the ability of the process corresponding to within subgroup variation i.e. a snap shot whereas Ppk indicates ability of the process corresponding to between as well as within subgroup variation i.e. a long shot? If that is the case Ppk appears to be more meaningful than Cpk.
Meaningful to talk about capability before a process is in statistically control?
Add one more thing:Cpk for short -term and Ppk for long-term
I think it is time that you start to refresh your knowledge?
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