I am most interested in hearing about the Keithley bridge. How do they do it? Just doing some quick calculations. At 1000 TOhms, 1 fempto amp of leakage into the null detector when balanced would cause an error of 1V. So with an 1000V supply, this means either the 1012 range switches in a 1 TOhm resistor for the low part of the bridge, or the alternative is the null detector leakage is way below 1fA. 1 attoAmp leakage would allow the top range resistor to be a much more comfortable 1GOhm.
These are just insane numbers! The designers of this stuff must come from another planet.
Is the 8 decade decade unit accurate to 8 digits or is it just 8 digits to provide the range? If it has a true 8 digit decade accuracy, it is something to bow down before. We are not worthy.
As far as the decade box goes, they probably have solid silver contacts. Before you touch the switches internally, the first thing you have to do is turn the switches end to end 10 times to knock off a bit of the surface tarnish. If they have been sitting in a store rack for several years before they were checked for calibration and the contacts were not exercised, they will definitely read high.
A very exciting buy. Lots of unobtanium in this lot.
Definitely get the UPS batteries charged as soon as possible, and sell it while you can. Just replacing the batteries will cost a fortune.
Richard.