Ok, I've slogged through a ton of old manuals and I've got a pretty decent crack at what the resistance reference requirements are for a large selection of old 6.5 and 5.5-digit meters:
https://github.com/USACalClub/gear/blob/master/dmms/README.mdAttached is a spreadsheet which summarizes all of the different sets of required references, and which meters require then.
Second attachment is an attempt at consolidating those into a smaller number of mailable "kits" which could be produced, and the meters which would be supported.
This was an interesting exercise. Requirements vary widely, and many particulars of the limits are often unspecified (e.g. many meters allow specifying arbitrary calibration values, but some of them don't state what the limits are of how far your artifact can deviate from nominal). Another example was that I had trouble figuring out which meters allow you to just calibrate the Ohms function, and which meters allow you to just calibrate one range of the Ohms function.
With the consolidated set, a few meters would get left out in the cold (assuming they can't calibrate just one range):
- Fluke 8846A (needs a 1G resistor, maybe it allows skipping this value?)
- Keithley 193 (maybe this can use 1.9x values instead?)
- Fluke 45 (the manual states this can use 1.9x values as an alternative)
- Fluke 8808A (appears to require 1R, 10R, 50R, 100R, 150R, 500R, 1k, 1.5k, 5k, 10k, 15k, 50k, 100k, 150k, 500k, 1M, 1.5M, 5M, 10M, 15M, 20M, 50M, and 100M)
(So, potentially, most of those which will be "left out" might be able to use alternate values anyway.)
Also, if anyone has an recommendations for very high value resistors (10M, 100M, 1G) which could be used, let me know (I have no experience here). Wirewound is probably out, and metal foils don't go that high either.
A relaxed requirement there would be a resistor which is stable enough that it can be used to simply transfer the meter's existing calibration back onto itself (e.g., read the value of the resistor before you start calibration, then enter that same value during calibration). If a resistor were immersed in a controlled 25C oil bath (+/- 0.01C), we could probably get away with fairly modest resistors for these high values. The point of including these "relaxed requirement" resistors is that some meters force you to calibrate all of the ranges, so if you are missing 100M, you are stuck. Being able to improve your calibration on 1k, 10k, etc, and simply copy your existing calibration for 100M is better than not being able to do any calibration.
Let me know if I've left off any important meters from the list so far! And as always, I'm very interested to hear any feedback here, as I'm pretty inexperienced here.
Thanks!
https://docs.google.com/spreadsheets/d/1VGwU2JbYxnRlgqtmr-_dVEWjddAojWWOSKOFVCrEPf8/edit?usp=sharing