I actually have a really selfish question regarding the next round of calibration send-arounds. My best multimeter equipment is a pair of Keithley 197s that I have worked somewhat hard to restore to life. One of them is very stable (all the way to ~ 5.5 digits or 220,000 counts), the other is not so stable and isn't even repaired yet. That said, I only need to calibrate one to check the other.
But one of my problems is that these meters use the 1.9 multiplier as the calibration points. So, at least in regard to the kind of calibrations that are possible without a super accurate voltage multiplier, the ranges that I have a chance of calibrating are the 200mV range (with 190.000mV) and the 2V range (with 1.90000V). Given that the reference we are talking about is 10V, I don't see a way to calibrate the higher ranges.
My current plan was to buy a bag of resistors to try and make a divider down from the best average value of the calibrator down to these two voltages, and try to get as close as possible to whatever ratio is required. Unfortunately the best equipment I have for this is also the Keithley 197's resistance ranges, so that seems like putting the cart before the horse.
The other possibility is that I can shoot for some value other than 1.9x that's easier to make with standard resistors (or resistors any of you guys have lying around), since the meter goes to 220,000 counts. I'm not sure I understand the impact this will have on the calibration, but I believe it's possible in principle. Since the procedure is to hook up a source whose voltage you know, and then make the display agree with that voltage you know, there is no reason I couldn't calibrate it at 2.0V. I assume this works in principle too for e.g. the 20V range: I could just try to calibrate it with 10V and make the display read 10V but I think would be a bad idea for a reason I don't understand (if anyone could tell me exactly why this is a bad idea, please do!)
In any case, does anyone have any advice here? Sending them off to be calibrated seems a bit silly, considering the cost of that is several times what I paid for the instruments in the first place. But if I could figure out a way to leverage the reference you're sending around, it would at least be a starting point.
The other reason I'm interested in this in particular on the low ranges, is that I think I once actually calibrated the 1.9V range on the 2nd meter (and hence mis-calibrated, because the meter is still broken). I would love, in particular, to fix that range.
Thanks a bunch!