STDEV within

STDEV () includes all the variation in the process is the an estimate of the variation within the subgroups. So with the you filter out the

• Drift of the process in time
• Tool wear
• Drift due different operators
• Drift due material batches
  

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 for the Cp and Cpk.

Legend

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

Formula subgroup size > 1

Legend

= subgroup
= sample in subgroup
= STDEV within
= 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