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Measurement, Test and Calibration Acceptance Criteria for Linearity

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Author  Topic: Acceptance Criteria for Linearity 
Neil Lurker (<10 Posts) Posts: 5 
posted 26 March 2001 03:27 PM
It is clear that the auditors are now expecting full MSA studies (i.e. bias, stability, linearity) not just Gauge R&R. What are you using for your acceptance criteria for linearity and why? Any insight would be appreciated. IP: Logged 
Atul Khandekar Forum Contributor Posts: 21 
posted 27 March 2001 08:15 AM
I think 'Goodness of Fit' AND the 'Slope' of Regression Line are the factors to look at. If there is a uniform bias over the range of the instrument, the regression line will be horizontal and if GofF is low, the line has no meaning. However, I couldn't find any guidelines as to the actual value at which the GofF can be called 'low'. Again, the slope of the line may well be zero and Goodness of Fit > 0.9, but what value of bias should be accepted? Help! IP: Logged 
Al Dyer Forum Wizard Posts: 622 
posted 10 April 2001 05:43 PM
Just from a practical point of view, As the result of a long term linearity study on a height gage, the following hypothetical results are realized. I base this on the simplified definition that linearity is the measurement of bias over the range of the gage. From 0  1" the bias is .0010 What is the acceptable criteria for linearity? I really don't know or care. My care: With the documented results I can determine which products/characteristics can be measured with the height gage. If my targeted dimension is .500 +/ .010 I "would" feel comfortable using the gage. If my targeted dimension is 2.500 +/ .010 I "would not" feel comportable using the gage. If my targeted dimension is 5.500 +/ .010 I "would" feel comportable using the gage. I don't know the correct term, is it the "10% discrimination rule" or the "10 to 1 rule" Am I making sense? Need help from the gurus! ASD... [This message has been edited by Al Dyer (edited 10 April 2001).] IP: Logged 
MSAFAI Forum Contributor Posts: 24 
posted 13 May 2001 07:44 PM
Hi guys, someone with a PhD in statistics told me a goodness of fit of about 0.7 is sufficient. About the slope of the line, I have the same question: how much is acceptable? Or maybe the linearity analysis is used just to estimate the bias at vaious working values? Anyone can help? MSAFAI IP: Logged 
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