The value of C_pk is the average of the lower and upper capability indexes; that is, C_pk = (C_pl + C_pu)/2.

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Quizplus · Accepted Answer

The value of $C_{pk}$ is not simply the average of the lower and upper capability indexes ($C_{pl}$ and $C_{pu}$). Instead, $C_{pk}$ is the minimum of the two capability indexes, which represent how well a process is meeting its lower and upper specification limits, respectively. $C_{pk}$ is used to measure a process's potential capability to produce output within specification limits, considering the process mean's shift from the target value.

The Value of Cpk Is the Average of the Lower

The Value of C_pk Is the Average of the Lower