Descriptions and Definitions of Quality Terms, Tools and Techniques

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Gage R&R

When using measurement devices we assume that they provide exact measures, every time. But gages can drift and may need re-calibration from time to time. Measures can also drift due to human factors such as variation in gage usage.

Gage R&R (or Gage Repeatability and Reproducibility) is an approach to ensure that the same measurement using calculations that measures the amount of variation in the measurement system due to variation in both the measurement device and the people taking the measurement.

Gage R&R is typically carried out before the gage is used with a new operator or situation.

Calculations are as follows (but are usually done with a statistical package):

Repeatability

Equipment Variation (EV) = r x R-bar
(r = 4.56 for 2 trials and 3.05 for 3 trials)

Reproducibility

Appraisal Variation (AV) = SQRT( (k x XDiff-bar)^2 - (EV^2 / n r) )

(k = 3.56 for 2 appraisers and 2.7 for 3 appraisers)

Repeatability and Reproducibility

R&R = SQRT(EV^2 + AV^2)

See also:

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