Gage R&R and Capability - Between 10% and 30% and cannot be improved


Michel Saad


I have once read (I think) that if the gage R&R is between 10% and 30% and cannot be improved, a correction of the capability indices has to be done. Does anyone know the formula to how the Cp, k and Cpk are corrected?


Michel Saad

For those interested, I found it (with no small effort I might add).

It is in the word file attached since I couldn't paste the image directly. It is only applicable to the Cp since % R&R is not dependent on the target.

I am intoducing into our Cp, Cpk, k policy that if a measuring equipment has a gage R&R between 10% and 30%, the equipment can be used but the Cp has to be corrected until the measuring equipment can be corrected.

Cpo is the measured Cp where Cp is the process capability once the measurement equipment uncertanty is removed. You will notice that for % R&R values of less than 10%, Cpp and Cpo are practically the same. It is for values of 20 to 30% that the formula is usefull.

Hope it helps.


  • formule correction du cp.doc
    14.5 KB · Views: 393


Fully vaccinated are you?
Thanks, Michel! The contribution is appreciated. I'm sorry no one here knew the answer. :thedeal:

Atul Khandekar

R&R to Cpk

This one I had downloaded from pdf zone or from dWizard's (I dont remember correctly). Its a small article on relationship between R&R and Proces Capability.

Hope this helps.

- Atul.


  • rartocpk.pdf
    17 KB · Views: 433
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