‘Navigation: Land, Sea, Air and Space’

Mr Blanchard's paper on Air Navigation Systems in the September 1991 issue of this Journal may give the impression that the Decca Flight Log was the first flight-desk map display to convert hyperbolic coordinates to a fair approximation to lat—long coordinates. A map display driven from GEE was built at TRE (Telecommunications Research Establishment) and demonstrated to PICAO (Provisional International Civil Aviation Organization) in 1946. The coordinate conversion problem was considerably simplified by representing the hyperbolae in polar coordinates having the master station at the origin. This technique was apparently independently devised by Decca, whose display was undoubtedly better engineered than TRE's experimental model, which made extensive use of Meccano and was unlikely, in that form, to appeal to aviators. Incidentally, reference 11 in Mr Blanchard's paper should be to Volume 32, No. 1 — not Volume 43, as was printed.