What is the difference between Cpk vs Ppk or Cp vs Pp?

As visible in the formulas the calculations are almost the same only for the Cpk and Cp the is used and for the Pp and the Ppk the s is used.

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

What is a subgroup?

If in a production process after every hour 5 measurements are done, the subgroup size is 5. When calculating the STDEV within data is ordered in groups of 5 to filter out the drift between the different groups.

But it includes the short therm variation of the process.

Cpk Cp

Ppk Pp

Variation Within the subgroups

Overall variation of all measurements

When use Cpk Cp or Ppk Pp

Cpk Cp

Ppk Pp

Once the process is in a state of statistical control

When you are initially setting up your process

The potential of the process capability

The actual process capability status over the time period

Short term performance

Long term performance

A process is in control when

Most points are near the average

A few points are near the control limits

No points are beyond the control limits

What if the process is not in control

Do a Gauge R&R and try to improve the measurement.