MarkF, that reply was to Fungus reasons of not installing the 500uV, my bad for not making that clear.
Forgot to mention that on 'Average' mode, the software zoom become important, because instead of showing steps of minimum 2 pixels (like in the 'Normal' acquire mode) on 500uV/div with averaging mode the minimum amplitude steps are 1 pixel, so one can see 50uV signal variations, which would not be possible to see at 1mV/div.
I didn't know some oscilloscopes can't keep the trace in view on 500uV/div, sorry to hear that. Mine can, maybe somebody else is lucky, too, so why not try it first. If it doesn't work, all the options can be removed then installed again without the 500uV one.