P
pagnonig
Dear All,
I've been through a lot of posts regarding Cpk and Ppk and the short/long term discussion on them.
Now, I would like to be sure I've catch the right practical meaning for both.
I'm collecting individual measurements to be plot in a I-MR chart.
having USL and LSL limits I would compute Ppk for this process using the Sigma (n-1) calculation and not the estimator R.avg/d2 because in this case I do not have subgroups.
Therefore I would say that Cpk is meaningless for Individual readings.
Anyway, I've noted that both the estimated and the calculated standard deviation tend to be the same value as the number of individual measurements becomes 50-60.
Any comments on my approach?
Thank you!
Giuseppe
I've been through a lot of posts regarding Cpk and Ppk and the short/long term discussion on them.
Now, I would like to be sure I've catch the right practical meaning for both.
I'm collecting individual measurements to be plot in a I-MR chart.
having USL and LSL limits I would compute Ppk for this process using the Sigma (n-1) calculation and not the estimator R.avg/d2 because in this case I do not have subgroups.
Therefore I would say that Cpk is meaningless for Individual readings.
Anyway, I've noted that both the estimated and the calculated standard deviation tend to be the same value as the number of individual measurements becomes 50-60.
Any comments on my approach?
Thank you!
Giuseppe