(Attachment Link) A short comparison of channel noise, maybe not quite correct, but if you have some suggestions...
Some constraints:
2 mv because Rigol cannot go under this value without BW filter(automatic)
2 ns because Keysight cannot go more.
Also touch screen noise of RTB2002 compared with Rigol's touch screen noise.
For Hydron: Now I have attached 2 more pics that include Std. Dev values. For Keysight it was std. dev from the beginning, because it was not capable to correctly measure RMS value(no edges).
Few suggestions:
Always use same timebase, timebase will influence frequency content of the noise, and noise is not same for all frequencies. 2ns/div is too short, I would measure at 1ms/div, that would grab most of the spectrum and filter out 1/f noise..
Also, you need (like Hydron well said) to measure Stdev (or AC RMS in Keysight talk) to filter out DC component from RMS measurements.
I suggest allways measuring Mean (DC average, DC component, offset in this case), RMS (full), AC RMS (Stdev, only AC component), and P-P.
That way you have quick sanity check, because all those numbers must cross check..
When in doubt, you can always compare P-P as quick check for order of magnitude comparisons.
Also, always compare with same bandwidth settings, and same vertical sensitivity settings.
Measure at several vertical sensitivity settings, and pay attention how S/N ratio changes and some scopes are better at some settings than others that might be better at some other settings.
Make a table ( on paper or Excel ) and write down all measurements. Than you can really compare.