I'm testing a little to measure how the voltage measured by Rigol, the voltage added from the power supply, and the current develop.
It seems that even after a few seconds the range of this error decreases.
For me:
At the lowest voltage.
28.90V and 25mA from the power supply
DM858 starts at 1.085V and when I leave it on, it starts to drop rapidly.
At the highest voltage.
32.91V and 33mA from the power supply
The DM858 measures a slowly decreasing voltage from 87.00mV.
If I play with it a lot, the range where it is not good has narrowed.
Good little advertisement.
(from -1000V to 25V) and (from 50V to 1000V) can be used safely, but between 25V and 50V requires extra attention.
Unfortunately, I could only test between -120V and 120V.