Well, maybe I shouldn't really be surprised. It's been hovering around the 10.0000000V on the P6048 for a while now. Typically +-.25ppm to maybe +-.5ppm off of the nominal 10V. Pretty mind blowing, and which I didn't really expect.
But again, if I dial in 10V on a different range, I'm nowhere near that kind of agreement. Which tells me the last adjustment of this instrument was primarily done at the 10V point on the 100V range. I welcome other thoughts.
Very, very, very satisfying. I've been in the restoration "business" (= invested hobby) for a good number of years now, and there's a lot to be said about "reforming" caps (by which I mean running the unit a generous amount of time to allow the wet caps - those not replaced, and most should, depending on age of unit ad other considerations - to regain their fitness), expelling moisture from units that sat around for a long time, etc. All units just want to be run with some frequency through their lifecycle to maintain good performance. There's no exception to this rule.
On the repair side - or maybe, long term service endurance - I receive parts to replace most power resistors today. It's just dutiful care for an exceptional instrument which, as they tend to, comfortably exceeds its spec. Another aspect I should mention is that, due to where I live (Southern California) I think I'm extremely lucky to run into very well cared for units. The incredible wealth of labs around here is amazing.