I can't test anymore as I don't have any dreambox's these days.
But both of my Dm7000 and DM800 the BER used to move alot, and I used to tweak my motorised dish using it knowing when it was on 0 it was getting the max signal. I used to find it very handy too for the weak sats (7°w for example) as I knew if the BER was under 2000 (from memory) the picture would be watchable.