A Tale of Two Precision to Tolerance Ratios

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Thanks so much for reading our publication. We hope you find it informative and useful. Happy charting and may the data always support your position.


Dr. Bill McNeese
BPI Consulting, LLC

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Measurement Systems Analysis/Gage R&R

Comments (6)

  • Angela Lopes PintoApril 1, 2020 Reply

    Thank you very much for your calculation model. It makes clear how to prepare the internal release specifications.Congratulations, robust work.

  • KOTHANDARAMANJanuary 17, 2021 Reply

    very useful and relevant topic . thanks

  • Diogo MartinsAugust 6, 2021 Reply

    Thank you very much for the explanations. But I have one question: when running the R&R study, sould I consider the product specification or the process specification? I mean, for example, if I have a product that its drawing/specification defines a thickness range of 0.008" – 0.014". But my inspection procedure defines a thighter range for security (process specification), let's say 0,009" – 0.013". What tolerance should I use to calculate my R&R results?

    • billAugust 7, 2021 Reply

      It depends on who the "customer" is for the Cpk analysis.  Your external customer, you use the customer spec; for you, you use the internal specs. 

  • Daniel LundJuly 6, 2023 Reply

    Hello Dr. McNeese,
    It seems that the AIAG MSA manual has many such misinterpreted ratios and yet when I google critiques of AIAG MSA methods, I don’t find very much out there. To me the math speaks for itself, however many of my colleagues are dubious or don’t have a background in math or stats and if they don’t downright insist on following the AIAG MSA manual, then they ask why has AIAG been accepted as a de facto “standard” in many industries. I don’t have a good reply for them nor a list of contradicting critiques. I know that when I was in the semiconductor industry, we followed SEMATECH and ISMI methods which were supported mathematically and were in direct conflict with some of the AIAG MSA methods. Do you know of such a list of critiques or how one may go about acquiring such a list?

    Best regards,

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