# Z-Value (Sigma Capability)

Six Sigma – iSixSigma Forums Old Forums General Z-Value (Sigma Capability)

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• #39813

Member

Could I get an entire derivation of Sigma capability viz., Z-value, Z-bench,etc. & how it affects process from any of the experts?

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#122101

A.S.
Participant

Sigma levl of any process can be calculated using a formula
Sigma Level = 0.8406 + SQRT (29.37-2.221 X lnPPM)
Hope that thisis the required by you.

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#122103

Member

Does it include Z-Lt ? Anbu.If yes, how can we derive this ?

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#122116

Mikel
Member

All of this z talk is a bunch of crap. What you need is Cp, Ppk, and Cpm. Go read the Minitab help menus and come back with questions that show you have done that.
In simple terms
Sigma Level = zbench = 3*Cp
zst = 3*Cpk (a meaningless number)
zlt = 3*Ppk
And Cpm? It is the one that tells you about the economic waste of your process. And what is the zxx value in Harry speak? There is none, he is not smart enough to understand.

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#132233

Prin
Participant

Can the sigma levl of any process be calculated using formula …0.8406 + SQRT (29.37-2.221 X lnPPM.. even if the process is not normal (e.g. weibull distibution)?

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#132236

Mr IAM
Participant

Stan – Thanks for your enlightenment.  Now I am sure everyone will dump sigma and go back to Cpk.  Because we all want to learn from someone smart enough to understand.

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