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Project Management & Agile · Advanced

Process Capability

The ability of a stable process to produce output within specification limits, measured by indices such as Cp and Cpk.

Definition

Cp = (USL - LSL) / 6 sigma measures potential capability; Cpk = min(USL - mean, mean - LSL) / 3 sigma accounts for centering. A Cpk of 1.33 or higher is commonly considered capable.

Example

Cp 1.5 but Cpk 0.9 indicates the process is off-center.

Exam tip

Cpk <= Cp; Cpk accounts for the mean's location.

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