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STDEV within

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Cp Cpk % out of tolerance
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STDEV (formula) includes all the variation in the process formula is the an estimate of the variation within the subgroups. So with the formula you filter out the But it includes the short therm variation of the process.

Formula subgroup size is 1

If the data is not collected in subgroups the subgroup size is 1 this is the standard setting in Develve to calculate the formula for the Cp and Cpk.
formula
formula

Legend

n = n
formula = observations in range 2
formula = 1.128
formula = STDEV within

Formula subgroup size > 1

formula

formula

formula

Legend

formula = subgroup
formula = sample in subgroup
formula = STDEV within
formula = with d = (subgroups x (subgroup size -1)+1)

How to use subgroups?

When subgroup size of 5 is selected behind the % Cp Cpk selection box, then row 1 to 5 is for subgroup 1 and row 6 to 10 is for subgroup 2 etc.

Data file