A First Course in Quality Engineering, 2nd Edition

342 A First Course in Quality Engineering

An example (from Boyles 1992) that assumes the usual two-sided specica-

tion with the target at the center of the specications is shown in Figure 5�20�

In this gure, all three processes (A, B, and C) have the same specications

and target but have different process means and standard deviations�

Looking at Process A, when the process mean is at the center of the spec-

ication, which is also the target, the values of C

p

, C

pk

, and C

pm

are all the

same� In Processes B and C, when the process standard deviation decreases,

the C

p

values increase, but the values of C

pk

and C

pm

are smaller compared to

C

p