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QuintSonic 7
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Process capability index (Cp)
The
cp
index is a measure of the spread of the readings as related to the specification limits. Only
the spread is of importance here. The
cp
index is calculated as follows:
s
LSGL
USL
Cp
6
where USL = Upper specification limit
where LSL = Lower specification limit
Process capability index (Cpk)
In addition to the spread, the
cpk
index also takes into account the location of midpoint as related
to the specification limits.
s
LSL
x
Cpku
3
s
x
USL
Cpko
3
Cpk = Min
Cpkl, Cpku
where USL = Upper specification limit
where LSL = Lower specification limit
.