Cpk vs Ppk - Part 3

Actually, there is nothing so special about Cpk and Ppk. Both numbers are figure out from the same formula as below



This is how Minitab figure out the magic number.
The only different is Sigma (within) and Sigma (overall)

How to get the Sigma (within) and Sigma (overall) then?

Honestly I am not really sure how Minitab estimate the Sigma value, I tried to figure out the Sigma value on Microsoft Excel with reference to Minitab help, I only manage to get which is very close to what Minitab reported, but so far I never get and exactly answer. Here is the answer of Sigma (within) & Sigma (overall) from my manual calculation.

Correct me if I m wrong.

Last update : 06/09/08