Wouldn't it be half of that due to the differential? In my understanding you either have to rotate both outputs 1 rev each, or lock one output and rotate the other one two times.
(Oh, by the way, here is a classic film about the pripciple of a differential, great if you need to explain it to somebody:
http://www.youtube.com/watch?v=K4JhruinbWc . Skip to 2:00 if in a hurry)