Calculation of the processability index Cpk

The Cpk value is determined from:

• µ = average value of all measurements
• s = standard deviation of the measurements

D represents the smaller interval of the average value µ to one of the limit values. With real magnet measurements the interval to the lower limit value represents, in most cases, the smaller interval.

Cpk = D / 3s

A fail-safe production with a theoretical overshooting of the tolerance by no more than 64 ppm (or 32 ppm for one side respectively) can only be guaranteed for Cpk >= 1,33.