Why the six, why the sigma?

It's a statistical term. (You'll find 'sigma' in all manner of standard deviation calculations - or, for the less mathematical, the capital sigma is that sign in Excel that adds everything up.) It refers to instances of defects in a production or services environment - usually relating to a process - such as that there are no more than 3.4 defects per million instances. Five or four sigma would be higher levels of defects but six is the standard.
Is this sounds convincing? if No please make sure to write your version in comment.

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