The one in the video is caused by the voltage drop on the internal wires. Can be fixed by a thick bridge between the GND of the channels 2 and 3. Ideally the bridge would be a thick copper wire soldered between the two GND connectors internally, but can be as well an external bridge between the two GND banana plug.
That's more like a theoretical corner case. In real life you would see more errors caused by real wires going to real circuits, so yeah, could have been better but doesn't really matter.
About calibration, I think that is supposed to be made in an automated way, it would take a lot of time and patience, and be very prone to errors to calibrate manually. AFAIK there are over 400 points to measure, read, then introduce manually
- 48 measurement points for CH1 VDAC
- 48 measurement points for CH1 VADC
- 32 measurement points for CH1 IDAC
- 32 measurement points for CH1 IADC
- same for CH2
- same for CH3 except VDAC and VADC are only 18 measurements each instead of 48
On the CD that came with DP832 there is a "DP80_CaligrationGuide_EN.pdf" that says it is recommended to calibrate once a year but they also wrote:
RIGOL does not recommend manual calibration by users. If calibration is required,
please contact RIGOL customer service department or the local distributor.
As a side note, my DP832 have some small errors, but I never calibrated it because it doesn't matter for my needs, and wires will introduce more errors anyway. Also I'm not very sure about the correct calibration procedure, and how big exactly is the calibration table (how many calibration points are), I've seen contradictory info floating around. In the programming manual there are no calibration commands, but from the disassembled firmware by tv84 there are hidden SCPI commands for DP800 calibration:
:CALibration:SET
:CALibration:MEAS
:CALibration:STORe
:CALibration:CLEar
:CALibration:STARt
:CALibration:END
:CALibration:SENSE
:PROJect:CALIbration:DATA:VOLTage:WRITe
:PROJect:CALIbration:DATA:VOLTage:READ?
:PROJect:CALIbration:DATA:CURRent:WRITe
:PROJect:CALIbration:DATA:CURRent:READ?
:PROJect:CALIbration:DATA:CURRent:ADDRess?
:PROJect:CALIbration:INFO:WRITe
:PROJect:CALIbration:INFO:READ?
:PROJect:CALIbration:INFO:ADDRess?