Gage Repeatability and Reproducibility (Gage R & R) is a methodology used to define the amount of variation in the measurement data due to the measurement system. Repeatability is due to equipment variation and reproducibility is due to inspector or operator variation.
Gage repeatability and reproducibility (GR&R) is defined as the process used to evaluate a gauging instrument’s accuracy by ensuring its measurements are repeatable and reproducible. The process includes taking a series of measurements to certify that the output is the same value as the input, and that the same measurements are obtained under the same operating conditions over a set duration.
Measurement System Analysis (MSA) or Gage R&R (Gage Repeatability and Reproducibility) is a method to control and assess a measurement process. It is useful to determine which sources are responsible for the variation of the measurement data. Variability can be caused by the measurement system, the operator or the parts.
The word gage (or gauge) refers to the fact that the methodology is aimed at validating instruments or measurement methods. For quantitative data, two characteristics are of interest:
Repeatability: A measurement is "repeatable" if the measures taken by a given operator for the same object (product, unit, part, or sample, depending of the field of application) repeatedly, do not vary above a given threshold. If the repeatability of a measurement system is not satisfactory, one should question the quality of the measurement system, or train the operators that do not obtain repeatable results if the measurement system does not appear to be responsible for the high variability.
Reproducibility: A measurement is "reproducible" if the measures obtained for a given object (product, unit, part, or sample, depending of the field of application) by several operators do not vary above a given threshold. If the reproducibility of a measurement system is not satisfactory, one should train the operators so that their results are more homogeneous.
A gage R&R study helps you investigate:
- 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.
The GR&R technique can be applied in most manufacturing-related measurement systems. It may be used as:
- A criterion for judging new measuring equipment
- A comparison among measuring devices
- A means for improving performance of measuring instruments
- A comparison for measuring equipment before and after repair
- A required component for calculating process variation and the acceptability level for a production process
- A measure of the need for training in how to use measuring instruments