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  • #52784

    Scott, Yim
    Member

    Hi, everyone…..
    I’m a SPC engineer in manufacturing
    I have a concern about Cp/Cpk…
    As you know, Cpk is calculated by means of meas and sigma.
    The sigma is estimated from Rbar/d2, normally.
    Normally, d2 is refer to reference table.
    But, I want to know that how to calculated d2.
    How is mathematical formula of d2???
    Please let me know about matistical formula of d2 …
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    #186129

    Szentannai
    Member

    Hi Scott,there is a theorem called “well – known” :) that states that the expected value of the range E(R) = d*stddev. (Thomas P. Ryan: Statistical Methods for Quality Improvement, p.123 ).To find the constant d all you need to do is to calculate the expected value of the range and the stddev and divide the two.The calculation of E(R) is generally quite difficult, but since Pearson there are tables for it. In case you’re interested in the formula that gets tabulated you can find it at this link. http://www.springerlink.com/content/a640k7526427lg3m/, its horrific :).Regards
    Sandor

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    #186174

    Lee
    Participant

    In regards to d2, there is a person on this site going by “Bower Chiel” that provided me with the formula for d2 and a spreadsheet to calculate d2 values.ย  The computations do not have to be re-created from scratch.
    Bower, I do not want to plagerize your fine work or not give you credit.ย  Please respond thread if you can.
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