Formulas and Tables

Capability indices

Capability indices use estimated sigma.

Cp

Cp for one-sided specifications

If you are using one sided specifications, use the following formulas to determine the Cp:

Upper specification

Lower specification

Cr

Cpk

f-cpk

Where:

Zmin is the smaller of Zupper and Zlower.

Using estimated sigma:

Cpm

Where: sigma for cpm

T = specification target (nominal)

Xi = a given individual reading of ” i ”

n = total number of individual readings

= symbol for summation