Anna,
The Process Capability Indices, Cp & Cpk - are probably the most common, but there are several others.
These indices give you an indication of how well a process is capable of meeting a set of spec. limits...

Cp - only tells you whether or not the standard process spread is capable of fitting within the spec.
limits.
Cpk- additionally, tells you how well a process is centered around the center line, process ave.

The formulas for both are:

Cp = ((upper spec. limit)-(lower spec. limit))/6*(std. dev. for process)

Cpk = min(Cpu, Cpl)         minimum of the following two formulas...

Cpu = ((upper spec. limit)-(process ave.))/3*(std. dev. for process)
Cpl = ((process ave.)-(lower spec. limit))/3*(std. dev. for process)

There are a number of good quality engineering & statistics books available that outline this in much more
detail.

Hope this helps,
Rob


Anna Miracle wrote:

> Ancillary subject, but I know somebody out there can enlighten me. Does anyone
> know what cpk means besides "process capability index"? Does "cpk" actually
> stand for something?
>
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