If i turn it to 80 it will change to 40 in the ND./Daniel

It is difficult to see on my bad picture. But it is set to 40

All is correct with that pic and range.

The range is set to 40, so the exact middle point of the display shows 20. Everything looks ok here. Or is this not what you're asking about?

Ok.. thanks for your fast reply :)But of course, the middle point is 20 :) Well you learn something new every day.Thank you for your response to my perhaps stupid question. But now i know how it works./Daniel

Not a stupid question at all! You learned something and got help, thats what the forums are here for!