Contents
- Index
Cpm
Capability index measuring the ability of the process to meet the specifications. Both variation and centering are considered. The formula is:
where USL is the upper specification limit, LSL is the lower specification limit, T is the target, m is the average and s is the standard deviation. Cpm is independent of the units of measure. The denominator of Cpm contains the Root MSE. Maximizing Cpm is equivalent to minimizing Taguchi loss.
Cpm is always less than or equal to Cp. They are equal only if the process is perfectly centered. In this respect, Cpm is similar to Cpk.