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5.15 in MSA

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  • #35587

    Nikunj
    Participant

    Hi
    can some one explain why  5.15 is used for calculating % tolerance in MSA. 
    Alifa.

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    #100480

    faceman
    Participant

    The 5.15 creates a 99% confidence interval based on your measurement error. 
    If you go to this Z table (http://www.statsoft.com/textbook/sttable.html? ) and look for the value 0.4950 you will find that the Z value is 2.575 (get the last digit by linear interp).  Double that (to cover both sides of a normal distibution) and you get 5.15.
    Regards,
    Faceman

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    #100481

    Ken Feldman
    Participant

    Relates to a z of 2.575 x 2 which encompasses 99% of the values.  Check out the z table.

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    #100491

    Bart
    Participant

    The wording is a little off.  In MSA, the value 5.15 doesn’t really have anything to do with confidence intervals. 
    Its just that the region 5.15 standard deviations wide and centered on the mean incorporates 99% of the population. 

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    #100504

    Gabriel
    Participant

    Go get the current edition of MSA and use 6 instead of 5.15. It seems that someone at AIAG finally noted that there was no logical in using 6 sigma to cover “about all output of the manufacturing process” and 5.15 sigma to cover “about all the output of the measurement process”.
    Now 6 sigma is used for both.

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    #100508

    Ken Feldman
    Participant

    Quote from Minitab 14:
    “Standard deviation component multiplied by 6. You can change the multiple from 6 to some other number in the Options subdialog box. The default is 6 because 6 is the number of standard deviations needed to capture 99.73% of your process measurements. The last entry in the Study Var column is 6*Total. This number, usually referred to as the study variation, estimates the width of the interval you need to capture 99.73% of your process measurements. Use the multiplier 5.15. to capture 99% of your process measurements.”

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    #100544

    Nikunj
    Participant

    Thanks all for the information.
    regards
    Nikunj

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