What is Gage Repeatability and Reproducibility?
Gage Repeatability and Reproducibility (Gage R&R) is a method used to determine the amount of variance in measurement data caused by the measurement system. The system compares the measurement variation with the total observed variability, thereby defining its capability. The two most important factors in measurement variation are repeatability and reproducibility. Repeatability is caused by equipment variation, and reproducibility is caused by inspector or operator variations. Gage R & R is able to make the following known:
- The difference between the measurement system variance and the process variation
- Operator influence is responsible for a large amount of variation in measurement systems.
- The ability of the measurement system to discriminate between parts
Why Perform Gage Reproducibility & Repeatability (Gage R&R)?
In any quality system, there are variations in the measurement data. Variation is inherent in all manufacturing processes. All measurements have some level of error or variance. To have the biggest impact on product quality, a robust SPC process needs accurate and precise data. We as quality professionals need to know what percentage of the variance is caused by the measurement system. Gage Repeatability & Reproducibility has been proven to be a reliable method of evaluating the capabilities of a measuring system. Gage R & R studies examine the repeatability of equipment and the reproducibility of appraisers. Understanding Gage R & R enables us to predict percentages or probabilities of measurement errors and identify the source (equipment, appraiser) of the variation. By determining where variations in the measurement system exist, we can improve the quality and accuracy of our data. Better data will lead to better decisions and fewer errors.
How to Perform a Gage Reproducibility & Repeatability (Gage R&R).
There are different techniques to complete a Gage R & R analysis. These are the two methods that are most commonly used to calculate Gage Repeatability and Reproducibility:
- The average and range method
- The ANOVA Method (Analysis of Variance).
This example uses a software program to perform the ANOVA. Both methods estimate three components of measurement error:
- Part-to-part variation
ANOVA calculations can be more complex, but they also allow for a better distinction between appraisers and parts. Most software programs include ANOVA. This information can be used to identify the major contributors to variation in our MSA.