Control Limits and Specifications: The Four Process States

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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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Comments (5)

  • AnonymousFebruary 28, 2022 Reply

    Thank you for the publication. its very informative

  • Pat Kennedy ([email protected])February 28, 2022 Reply

    A very good article, however, I have a couple of observations (as I would like to discuss this with my Continuous Improvement Team.Firstly, it would hav been good for the graphs to have shown the spcification target and limits (50+-15). It would help those learning about SPC control to easily see the process position.Secondly, Figure 6 where process variation is greater than engineering tolerence. To me if the natural tolerance is greater than allowable for the engineering tolerance then it belongs to State of Chaos as the process is incapable of meeting specification and requires improvement to return to a lower status.Finally, software is very good and I use it regularly.Keep up your good work

    • billFebruary 28, 2022 Reply

      Hi Pat.  Thanks for the kind comments.   Figure 6 – it is in statistical control so even if there is out of spec product, you can predict what will happen – not the case for Chaos where the process is out of statistical control.

  • Jessie RiversFebruary 28, 2022 Reply


  • Kenneth AsamoahApril 29, 2022 Reply

    Thank you so much for this article. It contains a lot of useful information

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