What is the difference between CP CPK and PP PPK?
Pp, Ppk vs Cp, CPK
Cp & Cpk use an estimate for the standard deviation using the R Bar / d2 method. Pp, Ppk are more liberal where Cp, CPK are more conservative. Use Pp & Ppk when you are initially setting up your process. Use Cp & Cpk once the process is in a state of statistical control.
Why is PPK higher than CPK?
The automotive confusion aside, Ppk will always be greater than Cpk since Ppk is long term capabliity and Cpk is short term capability. The only way that Cpk will be greater than Ppk (other than a misuse of the terms and formulas) is under the conditions stated in a previous post.
