Danny:-
....a special monitoring device in a corner of the airfield... Could this be the "camera obscura" we puzzled over long ago on this Thread ?
Indeed, Danny, my thoughts as well. That installation was of course set in the roof of the SHQ at pre-war Bicester. With it the assessment of practice bomb aiming on the marked a/f aiming point was possible with the release of the "bomb" (usually a Tate & Lyle syrup tin!), enabled by observing it on the projected obscura image, the release point showing up by means of the chemical contents of said tin. That was then compared to the DS solution, given the w/v stated, and the result awaited the crew back at the OTU. Perhaps technology had moved on at Windrush by then, Walter?
The now derelict structures that survive at many of these training locations have more meaning when they are identified for what they were, be it turret trainers, dome trainers, link trainer buildings, etc. They all played their part in this global effort to train aircrew for World War II.