At Bomber Command Bombing School, Lindholme c.1955 we had two H2S, Mk4a that is, not the Mk9 NBS trainers, that had glass plates about 4 ft square with mythical model terrain built onto the glass plate. The plate was put in a tank of water, and a crystal transmitter/receiver mounted on a 'crab' that was moved by X and Y coordinates, sent sound waves through the water. This was then fed into the normal H2S receiver and displayed on the fishpond indicator.
Above the 'crab' that carried the crystal Tx/Rx there another glass sheet, with a map of the model terrain below. A felt tip pen that left the track on the lower side of this glass, the pen retracted at the time of bomb release and rose with a clunk to mark the point of impact.
While I was working on this kit, I assisted the guys from EMI to install the 1st H2S Mk9/NBS trainer. This used a large, about 3 ft square, sheet of film and a photo electric system to achieve the same sort of simulation. The device held two such sheets of film vertically and was promptly nicknamed the 'Fish Fryer'.
We also had two Gee-H trainers that had 'bog roll' displays the same as a seismograph. The paper roll unwound at a rate proportional to the a/c speed and the trainer gave a kick to one side for when the bomb should have landed and a kick the other way when it did land. Errors were calculated in time for under/over shoot and in yards left or right.
This is as I remember it, but after 57 years, my memory is somewhat subject to errors.
