May  2002

Vol. 4, No. 5

Quality Quiz from Professor Cleary

You're right!


To get a negative Cpk, either Zupper or Zlower must be negative.

Consider A.



Consider B.

In both cases, there is a negative Cpk. A negative Cpk tells you nothing about whether your process average is outside the upper spec limit or the lower spec limit.


Copyright 2002 PQ Systems.

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