Cp

Cp is a measure of process capability that compares the specification width (USL – LSL) to the total process variation (6σ) for a given process or product parameter.  The higher the Cp value, the more potential a process has to fit inside specification limits.  Unlike Cpk, Cp does not take the process position (mean) into account, so a high Cp does not necessary equate to a capable process.  The equation for Cp is

Note that for a perfectly centered process, Cp = Cpk.

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