- Repeatability—How much variability in the measurement system is caused by the measurement device.
- Reproducibility—How much variability in the measurement system is caused by differences between operators.
- Whether your measurement system variability is small compared with the process variability.
- Whether your measurement system is capable of distinguishing between different parts.
For example, several operators measure the diameter of screws to ensure that they meet specifications. A gage R&R study () indicates whether the inspectors are consistent in their measurements of the same part (repeatability) and whether the variation between inspectors is consistent (reproducibility).
Examples of repeatability and reproducibility
Repeatability and reproducibility are the two components of precision in a measurement system. To assess the repeatability and reproducibility, use a gage R&R study ().
- Repeatability
- Repeatability is the variation due to the measurement device. It is the variation that is observed when the same operator measures the same part many times, using the same gage, under the same conditions.
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To estimate the repeatability of a Gage A, Operator 1 measures a single part with Gage A 20 times. To estimate the repeatability of Gage B, Operator 1 measures a single part with Gage B 20 times. Gage A has less variation, so it is more repeatable than Gage B.
The solid line is the measurements from Gage A. The dashed line is the measurements from Gage B.
- Reproducibility
- Reproducibility is the variation due to the measurement system. It is the variation that is observed when different operators measure the same part many times, using the same gage, under the same conditions.
- Operators 1, 2, and 3 measure the same part 20 times with the same
gage.
The three lines are the measurements from Operator 1, 2, and 3. The variation in average measurements between Operator 1 and 2 is much less than the variation between Operators 1 and 3. Therefore, the gage's reproducibility is too low.