Gage R&R, formally called Gage Repeatability and Reproducibility, is a measurement system/study used in conjunction with a calibration process to ensure decisions about a measurement (applying Statistical Process Control for instance) are accurate. Using precise and accurate data for process improvement applications is essential for successful systems. It is important to acknowledge all measurement data will have some percentage of variation. Combining this variation with product of process variation can result in a value that is inaccurate. The first step to ensuring that measurement data is accurate, it must be determined the amount of variation or inconsistencies considered acceptable. A tool that can be used to evaluate measurement is Gage R&R.
Several techniques exist for completing a Gage R&R study, but the two most common methods are the Average and Range Method and the ANOVA (Analysis of Variance) Method. Both methods focus three components of measurement error: repeatability, reproducibility, and part-to-part variation. Using the information, it will be easy to identify any major contributors to variation in the Measurement System Analysis.
The basic steps to a preparing for a Gage R&R study include:
- Addressing all known issues with the gage,
- Calibrate the gage,
- Check the gage resolution,
- Collect samples to be measured, and
- Ensure samples are not identifiable to the operators.
After conducting a Gage R&R study, a percentage will be calculated to represent the variance. The goal is to have a variance of less than 10 percent and an unacceptable level of variability in the measurement process is one that is greater than 30 percent.