Gage R&R Required on Micrometers and Calipers?



micrometers and calipers

I know someone has the answers, but need to know if GRR's need to be done on micrometers and calipers under the new standard? If it is, how does one do perform it if they are digital and the operator sees the reading instead of actually reading them. Would like an expert opinion.

Al Dyer

Other than ISO, I don't know of any standard that would not require you to perform R&R on a type of gage used to monitor accept products and processes.

Assuming proper calibration there would be no difference between performing R&R on digital or manual gages. The goal is to measure operator and gage variation. For better or worse, I believe we are experiencing the final days of non-digital gages.

Any gage guru comments? I'm somewhat limited to auto and manufacturing trains of thought.

Atul Khandekar

The goal is to measure operator and gage variation
Al has said it all. The readings may vary due to the methods used by the operators. How is the job handled/held? With digital instruments, the possibility of error occuring during 'reading off' is eliminated. So the Appraiser Variaton may reduce.

Ryan Wilde

I've done uncertainty studies on calipers and micrometers, including the electronic ones, and an GR&R is very appropriate. The switch point of electronic readouts, combined with different operators, will produce measurable R&R results.

Calipers have slight amounts of play in the carriage/bar mating surfaces, and different operators will naturally use different closure forces to obtain measurements.

Micrometers will also show variance from operator to operator due to closure force (even with a ratchet or friction drive). Another issue with micrometers is the mating of the rotor to the spindle, which can become loose over time and show a repeatability issue.

One more log for the fire - different manufacturers provide different results, including electronic units. This would suggest that a GR&R would be necessary for each brand, each type, and each size of device.



Uncertainty measurements for 17025 can go beyond just R&R. R&R is probably the most important (and largest) component of uncertainty, but there may be other factors that contribute such as temperature (expansion of gage and part measured), variance from nominal in the standard used to calibrate the gage (i.e. 1" gage block was actually 1.000002") and so on. Another component is the least significant digit error on a digital gage. Rounding error could be 50% of the LSD.

Check out There is an uncertainty calculator that may have examples to help you.

Much of the requirement depends on if you are using the gages to accept production parts (gage R&R should be enough), or are a laboratory certifying parts for a second party under 17025 (need to go beyond).


Ryan Wilde


The uncertainty calculator has been updated, and you can get v3.0 at . It is a major upgrade, and as you know, v2.5 was a great program. The new software easily rivals any commercial software for functions and useability, and this is STILL FREEWARE!!!! :D BTW, Chris Grachanen is my hero.

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