# 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