Oh stupid of me !
Than it makes sense of course. And now I managed to adjust them correctly (there was a 0.05v drift).

> Others may correct me, but I think you misunderstood the adjustment
> description: As far as I understand it right this is not a trimming to
> absolute 0.000V +/- 1mV, but the voltages should not vary more than 1mV
> in relation to each other.
>
> Florian
> --
> http://fa.utfs.org/
>