snip....
What would come back however would be a vref or better the two with some usage, aging and hopefully less ongoing drift with a known uncertainty by a much better meter. These then applied because of the additional resolution of the 7510 against even @meds Siglent should give a suitable reference point on the last digit bieng correct or not.
While for repairing of gear the extra resolution may not be needed if you want to make a widget you know is right to the last mV you really need stable gear to 0.01mV resolution and accuracy to test your widget against.
I really doubt that you can have much faith in using another meter, even if it has those extra digits, the readings acquired against meds references, would still be different from the references that med can get and repeat using his equipment. Lets say they are checked using the 7150 and the readings passed over to med, then he gets his hands on a calibrated 7150 for his own use, he is still likely to get completely different readings on the 7150, unless that meter was set up using the very same references as that of Kj7e, as the factory is likely to have more than just the one calibrator. Then if the meter has been sent to off to another calibration lab for re-certification, it will be checked and adjusted against yet another reference source.
Faith implies belief is some mythical sky ghost so clearly the wrong and inappropriate choice of words. While I am aware of your view on precision bench requirements or lack there of for some things and people it matters.
Not sure for example where @med got to with his higher voltage standards for his own meter calibration but if you are multiplying errors from unknowns then it matters even more. Using an unknown source for me was always the biggest issue with these.
Meters when calibrated are tested against one calibrator which is in turn calibrated against known standards if not sent to a lab with a JJ array among others. Keysight in Oz send their calibrators out to be done. It will make ZERO practical difference if a meter is tested a different bit of gear or not as they are another 1 or 2 levels up again. PPB against PPM level gear. The important thing here is ALL calibrators are traceable and have KNOWN levels of certainty.
The DMM7510 because of it's traceable calibration has CERTAINTY of measurement which has an actual number to work from. At 10V DC it is specced to 9-14PPM+1.2 for range (90 or 1 year spec) so assuming a source in that range it will be accurate and have good certainty within a range of 9.999985 and 10.000015.
The best meter (resolution wise at least) @med has is the Siglent and at the same 10V it has a spec of 0.017% which puts it at 9.9983 to 10.0017 so any returned reference with a known figure from the 7510 will be way better than @meds meter can resolve and therefore an appropriate standard to reference against. This obviously implies same temp and the reference not drifting post testing.