Gage Repeatability And Reproducibility (Gage R & R)

Gage Repeatability and Reproducibility (Gage R&R) is the amount of measurement variation introduced by a system of measurement that consists of a measuring instrument itself and the individuals using it.
It quantifies three things:
1. Repeatability – variation from the measurement instrument
2. Reproducibility – variation from the individuals using the instrument
3. Overall Gage R&R, which is the combined effect of both of the above
The Gage R&R is normally expressed as a percentage of the tolerance for the CTQ being studied, and a value of 20% Gage R&R or less is considered acceptable in most of the cases.

Example:- for a 4.20mm to 4.22mm specification (0.02 total tolerance) on a shaft, Gage R&R value would be 20 percent of 0.02mm (0.004mm)
For example, while reading an outside thermometer, one shall find a Gage R&R of 5 degrees that means observation up to 5 degrees of temperature deviation, independent of the actual temperature at a particular given time. However, the thermometer might also be calibrated 10 degrees to the lower side that means on average, the thermometer will read 10 degrees below the actual temperature. Poor accuracy and high GR&R depicts that the measurement system is useless.
Measurement system variation is often a major contributor to the observed process variation, and in some cases it is found to be the number-one contributor.
Six Sigma is about reducing variation.
If a high-variation measurement system is not calculated and corrected during the Measure phase of a DMAIC project – there is a chance that the team will be puzzled by the deviation they encounter in the Analyze
Purpose
Factors affecting a measurement system:
• Measuring instruments, the gauge or instrument itself and all mounting blocks, supports, load cells, etc. The easy use of machines, the disorganization among different parts, and zero blocks are few examples of sources of variation in the measurement system. In systems creating electrical measurements, analog-to-digital converter resolution.
• Operators (people), the ability and/or discipline of a person to follow the written or verbal instructions.
• Test methods, the set-up of the devices, the test fixtures, how the data is recorded, etc.
• Specification, the measurement is reported against a specification or a reference value. The range does not affect the measurement, but is an important aspect in calculating the viability of the measurement system.
• Parts or specimens, some items are easier to measure compared to others. For example, a measurement system may be good for measuring steel block length but not for measuring rubber pieces.
Anova gauge R&R is an important tool in the Six Sigma methodology, and it is also a requirement for a Production Part Approval Process (PPAP) documentation