The Norden didn't control the airplane, there was another device(the Auto pilot) that did that. Not all planes were equipped with an Auto-pilot and a Norden(or Sperry, for that matter) Bombsight. Some had one, some had none.
We don't want to get too accurate on the bombsight for several reasons, prime being the complexity of the instrument. Here is a brief description of "greening up" the Norden:
Level Gyros(which is a whole 'nother process)
Enter via dials:
Bombing alt.
Bomb ballistics.
Air speed.
Air Temp.
Barometric pressure.
These settings partially synchronized the (bombsight's) telescope's Mirror with the aircraft's movement over ground.
Next the bombadier killed drift caused by the wind, using turn and drift knobs to fly the aircraft(through the auto-pilot).
Then he killed rate by adjusting the rate knob(of course), this completed the synchronization between the mirror and the ground, leaving the target apparently motionless in the viewfinder.
Finally, the bombadier used the displacement knob to center the target in the cross hairs.
From here, the Sight and the Auto-pilot would fly the plane to the drop point and release the bombs. Any (flight)deviation from true broke the synchronization and the ability of the sight/autopilot to guide the plane to the drop point.
The second reason we do not want too accurate a representation of the Norden sight is it's appaling lack of accuracy. They didn't fly large groups of bombers for protection from fighters; They flew them because it was the only chance they had of damaging the target.
All info paraphrased from "America's Pursuit of Precision Bombing, 1910-1945", 1995, Stephen McFarland.
Lizking