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Zlt

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Definition

The long-term z-score, Zlt, is a long-term process capability metric. It is the distance in Standard Deviations (sigma) between the long-term process mean and the closest specification limit. It is calculated by subtracting 1.5 (the widely assumed long term process drift) from the Zst, or by using long-term data in the function: (Spec limit - Long Term Mean)/Long Term Std. Dev. Long-term data is obtained by taking Samples which take into account sources of Common Cause variation as well as Special Cause variation. Zlt can be used to estimate DPMO.

External Links

http://www.isixsigma.com/library/content/c010701a.asp