VANOS Physical Mechanics?

After installing my new P/P N54 head, I was using the timing tool kit and valve spring depressor and bearing ledge alignment vices I became curious about the Vanos Units that have a single bolt attaching them to the end of both the INTAKE and EXHAUST cam shafts. In looking at the gears on the Vanos units I can't see where the gears themselves would be able to move independently of the camshaft or even within the vanos unit itself. And the torque spec is so damn tight that I can't see the entire vanos unit being able to move independent of the camshaft either. I must be missing something. How can the mechanical timing be variable if the timing chain is wrapped around the vanos gear sets which are fixed on the camshafts??? Does this make sense?

In this picture (Non N54) you can tell the Vanos Cam Gear can be phased/moved independently of the cam position.




However, in this picture you can see that the gears on the N54 unit can't be phased on the vanos unit.