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Capability indices

Capability indices use estimated sigma.

Cp

cp formula

Cp for one-sided specifications

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

Upper specification:

cpu formula

Lower specification:

cpl  formula

 
 
 
Cr

cr formula

 
 
 
Cpk

cpk formula

Where:

Zmin is the smaller of Zupper and Zlower.

Using estimated sigma:

z upper formula z lower formula
 
 
 
Cpm

cpm formula

Where: sigma for cpm

T = specification target (nominal)

Xi = a given individual reading of " i "

n = total number of individual readings

= symbol for summation