My board arrived this morning.
I'm about 1/3 of a mV out at 10v on the Keithley 2100 about the same the other way on the PM2525. (I had to swap the power leads round).
I haven't checked the specs on a Keithley 2100, but that difference seems quite large. Was everything warmed up for a while?
The closeness of my results I think was slightly fortuitous as my study was quite warm (from equipment running in various experiments I'm doing) and I think RoadRunner calibrates at quite a warm 24C (that is from memory - perhaps I have that wrong) but I would still expect the variation to be a few 10s of microVolts not 300 or so.
It was on for hours. I've had it on again tonight and it's 9.99954 now
So my only other reference is a £4 10v ebay reference so show here 2nd we get..
So 2100 reads 9.99954 & 10.00590
The PM2525 reads 10.002 & 10.010
The UT60E reads 10.00 & 10.01
The UNI-T 4102C reads 9.99 & 10.00
Now we have 9.99965 when I switched it on cold it read 10.00118
It is just sat on the desk connected to my bench power supply which is set to 15.00123 (using the 2100)