Gage R&R is the study that examines the variation produced by a measurement system by separating it into two components. It is the most common application within MSA.
Two components
Repeatability: The difference between the results obtained when the same operator measures the same part repeatedly with the same instrument. It is the variation originating from the instrument.
Reproducibility: The difference between the results obtained when different operators measure the same part with the same instrument. It is the variation originating from the operator and the method.
How is it conducted?
Typically, several operators measure a set of parts representing the actual variation of production, in random order and more than once. It is important that the parts are spread across the tolerance range; if they are all very close to each other the result is misleading.
What does the result mean?
The ratio of measurement system variation to total variation or to the tolerance width is calculated. If the ratio is high, the measurement system is not reliable enough for decision-making.
In that case the capability indices and control chart signals are also questionable. Gage R&R is therefore the precondition for process capability studies.
The results are reflected in the control plan and the PPAP package.
Planning and conducting a Gage R&R study and interpreting the results are practised on real data sets in the MSA training. For the effect of measurement reliability on process control, see the SPC training.