I got a Keithley 182 nanovoltmeter with a display failure a few days ago, which is easy to fix by making a simple 60V boost converter. Then I did some simple tests on this instrument. Unexpectedly, I got a very interesting (strange) result.
In short, in the 30V range, near
3.25V 5.2V, the voltage measurement has a sudden jump about 100uV. I have repeated this many times in the past, and the results are the same, no matter how I change the filter, integration time, or other settings.