In a nutshell, yes. I think it depends on the number of credit hours the class is, and the averaging is done with the honor points.
Forgive me if I have simplified too much here, but this is the method I used to figure mine out: A D is worth 1.0 honor points, so a D in a 3-credit class is worth 3 honor points. A B (3.0) in that same class is worth 9 honor points. Average the two and you get 6 honor points, which is a C (3 credits x 2 pts).