If you want to get technical, this topic is better dealt with by others since it is a quality matter rather than dimensional metrology where I hide out. But, disputes go on every day over measurements and sometimes resolving them can be quite challenging—when possible. Yes, there are protocols in this area but when the shouting stops it always comes down to basic metrology so that’s my excuse for wading into treacherous waters.
I would be remiss if I didn’t offer some advice to avoid such disputes in the first place. The easiest way is to determine how your customer will check what you’re supplying before you switch on the machines. If they have better toys than you, you’ll have to upgrade. If they have worse or don’t know what they’re doing, you could get technical and point this out to them to avoid future battles. If they don’t like to hear this, you have to revert to politics. This means get them to agree with you using the same methods and hardware they are using and ignore the metrology involved. The product measurements may not be worth squat, but at least you won’t be fighting over it. And if they discover this, you’ll have their agreement on method to cover your end. Not the way things should be, but remember it’s politics so you know how that system works.
I’m assuming the dispute is between you and your customer and that your gage or instrument is being hung out to dry in the process. Being the clever type that you are (like all my readers), you fire said suspect off to a cal lab and get a report back indicating it’s good. However, your customer won’t accept this and does the same thing with his ‘go to’ source for calibration and their report says the item is not as good as your source says it is.
The good news in all of this is that you and your customer are not engaging in hand-to-hand combat over it. Paid mercenaries—the cal labs—are now on the front lines and become the targets.
Save time by advising both labs of the dispute and give them the opportunity to review their work because someone could have been having a bad hair day. After all, they’re using humans (usually) and we know they slip up sometimes. Similarly, the digital wonder one of them used may have lost a digit along the way. Assuming both will fight to the death over their results, another approach may be required.
One approach is to have both labs agree on a third party lab to do the work and whichever set of numbers closely matches theirs, a winner can be declared. You should get agreement on who will pay the third party for their work, but usually, the loser pays. Depending on the calibration, you could send the disputed item off to NIST if it is something they usually do but be prepared to wait for it and expect a much higher bill than you get from a local lab.
The reports issued by the labs should be shared and reviewed to see if the labs are ‘equal’ in capability. This means a check to see if their accreditation matches the work they have done. And speaking of accreditation, it is a given that if they don’t have any, all bets are off.
Take a hard look at the scopes of the labs involved. If both are accredited and show practically the same uncertainties, there’s a possibility someone’s assessor wasn’t up to speed on the metrology part of the process so a check of the actual hardware used can be revealing. Sometimes assessors and/or quality auditors are dazzled by expensive all-singing-and-dancing digital hardware that is not up to speed from a metrology point of view despite clever software and tweaking. It could be that the device is providing a derived value rather than a directly measured one or is set up using a dodgy master that doesn’t directly replicate the feature being measured such as pitch diameter.
Like all disputes, you have to go back to the basics to sort things out.