Yield and quality control

Which process capability index is used when the process mean is offset from the center of the specification?

  1. ACp
  2. BCpk
  3. CMTTR
Show answer and explanation

Answer: B. Cpk

Cp assumes the mean is at the center of the specification, whereas Cpk is obtained by dividing the distance from the mean to the nearer specification limit by 3σ, so it accounts for the offset. If the mean is at the specification center, Cp and Cpk are equal.

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