Hey -- I have an 03 996 tt and I have the exact same knob in my car -- I also cant figure out how exactly it works. Turn the outer ring one way and there is a light that turns yellow, turn it the other way and the light is green. Probably signifying the difference between city and highway but which is which? I have no idea. Also, the thing beeps all the time when it is on and I wish it would be quiet and alarm only if there is radar etc. Do you have any idea how good this model is or which model it actually is?