Finding angle btw normal vector and curves

I want to find the angle btw normal of the windows and curves. I calculated it but it gives me numbers larger than 90. It can not be. For example the degree 150 actually should be 60 (150-90). But why it did not appear like that?

Is this what you want? (5.3 KB)

It was not. But I handled it by writing a python script. Thanks.