Thanx, but it looks nothing like that !.It has the standard sort of backplate and the sensor is just fitted to the side on the plate.The rota looks like the normal rota but has two prongs on opposite sides.
It just has the markings DG stamped on it.
The sensor has got a magnet in the middle of it.
I can't understand how you would set it up with two markers on it.
Over to you