I am a newbie and need to do a simple thing, which I tried finding the solution to not avail.

I added Nurbs curves, I can pick the radius, which is fantastic. When I add a curve, should I assume that at its default without editing or playing with it that it is a fraction of a perfect circle? If so, what’s the fraction in degree? How can I change the size of that fraction? If I want half a circle, a quarter, or 1/12 of a circle etc. how do I do that?

Any help will be welcome.