While Vol. IV focused on variable gauge performance, this installment of “The War on Error” presents the study of attribute gauges. Requiring the judgment of human appraisers adds a layer of nuance to attribute assessment. Although we refer to attribute gauges, assessment may be made exclusively by the human senses. Thus, analysis of attribute gauges may be less intuitive or straightforward than that of their variable counterparts.
Conducting attribute gauge studies is similar to variable gauge R&R studies. The key difference is in data collection – rather than a continuum of numeric values, attributes are evaluated with respect to a small number of discrete categories. Categorization can be as simple as pass/fail; it may also involve grading a feature relative to a “stepped” scale. The scale could contain several gradations of color, transparency, or other visual characteristic. It could also be graded according to subjective assessments of fit or other performance characteristic.
While you may have been hoping for rest and relaxation, the title actually refers to Gauge R&R – repeatability and reproducibility. Gauge R&R, or GRR, comprises a substantial share of the effort required by measurement system analysis. Preparation and execution of a GRR study can be resource-intensive; taking shortcuts, however, is ill-advised. The costs of accepting an unreliable measurement system are long-term and far in excess of the short-term inconvenience caused by a properly-conducted analysis.
The focus here is the evaluation of variable gauges. Prerequisites of a successful GRR study will be described and methodological alternatives will be defined. Finally, interpretation of results and acceptance criteria will be discussed.
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