Also called gauge R&R, measurement system analysis, MSA
What is gauge repeatability and reproducibility?
A study that checks whether your measuring is trustworthy before you draw conclusions from the measurements.
What else it is called
- Other names
- gauge R&R, measurement system analysis, MSA
- In French
- répétabilité et reproductibilité des moyens de mesure
Related entries
Understanding gauge repeatability and reproducibility
Several operators measure several parts several times, and the variation in the results is split between the parts, the gauge and the people. The output is the share of your tolerance that is being eaten by measurement error rather than by the parts themselves.
It is the first thing to do when a quality problem is confusing, and the step most often skipped. If the gauge consumes 40 per cent of the tolerance, then parts near the limit are being accepted and rejected more or less at random, the capability numbers calculated from those readings are fiction, and the operators have already worked out that the gauge disagrees with itself and stopped trusting it.
Reproducibility problems are usually about method rather than people: where on the part it is measured, how hard the caliper is closed, whether it was allowed to reach room temperature. Those are fixable with a written method and an hour of training.
In practice
Before arguing with a customer about rejected parts, run this on the gauge you both use. More than once the answer has been that the two plants measure the same part differently.
Frequently asked
How many parts and operators does a study need?
The standard arrangement is ten parts, three operators, three repeats each. Fewer is possible for a rough check, but the numbers get unreliable quickly and the study is not worth doing badly.
Is a calibrated gauge automatically a good gauge?
No. Calibration says the gauge reads true against a standard. This study says whether it gives the same answer twice in the hands of your people on your parts. A perfectly calibrated instrument can still be unusable for a tight tolerance.