Motorola's math took into account a mean shift, which accounts for your ppm
discrepancy between 6 sigma and 4.53 sigma. In other words, the 3.4 ppm
equating to "6 sigma" allows the mean of the normal distribution to shift
1.5 sigma....and that's where the infamous Cp and Cpk values come into play.
So, it's tough to answer the original question, unless you set the mean
shift.
If this sounds complicated, it is, which is why many folks spent many hours
in 6 sigma class.
Good luck.
> ----------
> From: Brunker Ed[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Brunker Ed
> Sent: Tuesday, February 08, 2000 9:10 AM
> To: [log in to unmask]
> Subject: Re: [TN] Subj: Six Sigma
>
> 3 PPM DEFECTS MEAN 999997 good parts in a million. If a normal
> distribution
> curve means 1 miilion then as a decimal this is 0.999 997. Looking up my
> normal distribution tables for this I get 4.53 sigma, not six sigma.
> According to my maths tables 6 sigma is 1 failure in 1000 million. Now I
> know that Motorolla have altered the rules a little, but I don't quite
> understand how, (like including touch up / rework as normal manufacturing
> processes). Can anyone explain this little deviation from the maths
> tables?
> Regards
> Edward Brunker
>
> -----Original Message-----
> From: Hollandsworth, Ron [mailto:[log in to unmask]]
> Sent: Tuesday, February 08, 2000 1:41 PM
> To: [log in to unmask]
> Subject: [TN] Subj: Six Sigma
>
>
> Good Morning TechNetters!
> Here is a brain teaser for this early morning. Thinking six sigma. Six
> sigma is suppose to be 3.4 PPM. Good! Now what is five sigma, four,
> three,
> two , one. There is a chart that shows that relationship of a certain
> sigma
> and the PPM associated with that particular sigma value.
>
> Ok, the first five to get the right answer will be eligible to go on to
> the
> "Who wants to be a Black Belt" show. Enough levity, can someone help me
> out. Do you know the chart I am referring to? Can you send me the values
> and I'll make a chart.
>
> Grasshopper Ron
>
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