Capability Question

Six Sigma – iSixSigma Forums Old Forums General Capability Question

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    What can you derive from a control chart (ie XbarR) other than:

    Determine stability (ie OOC activity)
    Determine the sample descriptors mean and spread
    Calcuate std dev from Rbar / d2 or via xbar less SL  / 3
    Use std dev, mean, and SL to determine process capability 

    Can you get both Cpk and Ppk here?
    Demonstrate a shift in the process mean after a change
    I feel like there is more that I am missing…..


    Michael Mead

    There might be more, but you have the essesnce. What are you really looking for in an averagea nd range chart?
    It is a control chart because it is used to identify when significant changes to the process occur.  The capability information is almost an extra benefit since it is not related to control.  You watch the lines, compare them to your rules, don’t mess with the process unless the rules are violated.  Simple.
    Many people are tinkerers.  One of the benefits of the average and range chart is it keeps their fingers off the adjustment knob.


    Six Sigma guy

    Isnt it funny that subject and content are different :) ?
    Can we say control charts can be used for predictions in a way based on historical performance?

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