# Cmk is defined as a Capability Index for a Stable Machine

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#### SteveT

Could someone please describe to me what statistical index Cmk is, what it means, and how to calculate it.

Many Thanks SteveT

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#### freeda

Cmk is defined as a capability index for a stable machine. It uses the same formula as Ppk.
Cmk is a short term study of a machine capability. Whereas Ppk is a short run study for a process.

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ASD...

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#### Don Winton

I do not know about Cmk, but Cpmk is defined as:

Cpmk = (USL – LSL)/(6*(sqrt(StandardDeviation^2+(mean – T)^2)))​

Where T = Target Value.

This link (broken link removed) gives some additional info. This is a PDF file, so you will need Acrobat Reader to access it.

Hope this helps.

Regards,

Don

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I was better but I got over it.

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#### Don Winton

...what it means...

Ooops. Forgot. Cpmk is used when the tolerances are not symmetric about the target.

Regards,

Don

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I was better but I got over it.

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#### narfeldt

Ain't Cmk=revised rates of machine capability and calculates by the formula:

Cmk = 2((UTL-Mean)/(Xmax-Xmin))
Cmk = 2((LTL-Mean)/(Xmax-Xmin))
Cmk = the lowest value of above formula

Is this incorrect?

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/Best wish Narfeldt

[This message has been edited by narfeldt (edited 07 June 2001).]