I hereby affirm that I own 2 Windscreen Projectors - serial numbers 209 and 211. I acquired one from a fellow enthusiast 1991 and the other at a general sale as "unidentified". It was the first head up display giving bearing, range, and height directly to the pilot as against earlier radars that required an Observer to verbally communicate the information. It was probably manufactured by Barr and Stroud and was probably developed at RAE Farnborough by Arnold Hall. It was an experimental add on device originally for AI Mk V (Airborne Interception Radar) , and modified for AI Mk VIII but never saw service with either. It was integral with the very advanced AI Mk IX in 1942. The changing priorities of the air war, and the easy availability of the American AI Mk X workhorse meant that Mk IX was "put on the back burner" and abandoned in 1948. The 2 units I have are from Mk IX.