XbarS.CapabilityIndexCpk Method

Returns the capability index $c_{pk}$ .

public virtual double CapabilityIndexCpk(
double lowerSpecificationLimit,
double upperSpecificationLimit
);

The capability index $c_{pk}$ .

The capability index is

$c_{pk}=\min\left[\frac{\mathrm{USL}-\bar{x}}{3\sigma},\frac{\bar{x}-\mathrm{LSL}}{3\sigma}\right]$

where LSL and USL are the lower and upper specification limits, $\bar{x}$ is the center line, and

$\sigma=\frac{\bar{s}}{c_{4,n}\sqrt{n}}$