Re: R&R - Using Tolerance method, or part to part variation?
The one that you use depends on the gage use.
If the gage is used to inspect a part to specification, use P/T Ratio.
If the gage is used for process control such as SPC, or used for statistical studies such as a capability study, a DOE, a hypothesis test, etc. use %GRR (percent of total variation).
You can also search this forum for some more in-depth explanations that I have previously made for other posters.