The Nurbs surface rounds over my sharp edges. How can I get it to stop doing this?

After Constructing Grids in the Exact Surfaces tab

Open Exact Surfaces>Specify>Sharp Contours.

In this command you can pick the Contours or the Points that you want sharpened.

Selecting to sharpen a contour will change the line to a purple color.

The points will turn red if they are selected to sharpen.