0.0 is what i want :-).
In a desperate attempt I am now first writing 1.0 then 0.0 to everything, then afterwards set the values I computed, and in a final step I walk over everything and check if the values are what I think they are... and if they are not => exception
so rather abort than do something wrong.
but still  i am not really satisfied.

wish poser was open source :)