Curvature ++

It seems I need a curvature that can accept negative values. Then I can create a curve that goes from N to +N.
Thanks. 
@Skulpture we were talking about this in the old forum :) unfortunately not solved yet :(
and another post HERE talking with cinesmith. Well, me talking without answer. 
Ah yes back in 2010! I remember it now.

I wonder if this makes any sense for what you try to achieve?
I bring the min negative value to 0 by adding x. Then after curvature I subtract x. I am not sure if this makes Curvature behave differently though. 
@skulpture, I use limitscalevalue upside down,for input (limit min max) and output (output min max) for the curvature you have to stay with 0100, maybe needs some calculator`s,
best...bts