Bias and Linearity with Slip Gauge: Low R-Squared Value



Bias and Linearity

We purchased a New Digimatic Micrometer of a reputed make. We conducted the Bias and Linearity study with Slip Gauge, and we anlysed the result using the Regression. The R square value we got from the study if 0.69 as against 0.98. can any one comment on the study result. What might went wrong with the Micrometer as its new. At the same time we conducted GR&R study with this instrument and we got GR&R value less than 10%.


Drew H

Either there was an error in conducting the linearity study or the gage is very non-linear. Did you graph the results of the linearity study - could give you some idea of the source of the problem. The GR&R study is telling you things are consistent - i.e. repeatable. It gives the same measurement each time and the operators don't have any trouble making the measurement. I would look closely at the bias over the range of use and the linearity - if these don't meet manufacturer's specs, send it back!

[This message has been edited by Drew H (edited 07 December 2000).]

David Drue Stauffer

Hi. Just like to remind y'all that bias is defined as the observed average deviation from the target value (measurement standard) before any calibration adjustments are made to the instrument and thereby used to discern if there is a need to do an impact study on product acceptance. Sorry bout the long sentence. Linearity, is a study to determine the accuracy of a gage throughout its measurement range for the same purpose. All those calculated values really don't mean that much. The goal is to discover if THIS gage is capable of controlling your process to acceptable SPC Indices. IF there is a problem, then it becomes necessary to investigate to find out IF this has impacted product acceptance. Remember the tire company?
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