# Tolerance zone for Gage RR.

Six Sigma – iSixSigma Forums Old Forums General Tolerance zone for Gage RR.

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• #49565

jediblackbelt
Participant

I need help on a subject for “can’t tell zone” on my spec limits.  I have a note written in my manual from a few years ago that from the gage RR you can develop a band around a spec limit where within it you can’t tell good from bad.  My note says it is 2/3 x the standard deviation of the measurement system.  Does this sound familiar to anybody?  If so, could somebody elaborate if that is correct or how do you calculate it?

0
#169584

Mikel
Member

I have never heard of the rule, but there is some logic to it.2/3’s is leaves about 25% of the measurement error hanging out there
to hurt you. If you can talk your customer into doing the same on the
opposite side of the spec, you’ve reduced your odds of him calling
something bad that you’ve called good to almost zero.

0
#169585

Mikel
Member

I have never heard of the rule, but there is some logic to it.2/3’s is leaves about 25% of the measurement error hanging out there
to hurt you. If you can talk your customer into doing the same on the
opposite side of the spec, you’ve reduced your odds of him calling
something bad that you’ve called good to almost zero.

0
#169767

RonJ
Member

Hello, I think you’re talking about Probable Error. PE = 0.675 times your estimate of standard deviation. Dr. Wheeler wrote an article explaining this topic, “Relative Probable Error”.
http://www.spcpress.com/pdf/Relative_Probable_Error.pdf
Hope this helps.

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