I know John Farley could tell you lots about the early Harrier moving map - a series of 35mm slides of 1/2 mill topo maps mounted on rollers and driven by rubber bands (literally). I cannot remember how the slides were mounted, but say 8 to a line, and when you 'went off the edge' of the end slide, a great whirring noise occurred and the whole assembly rotated to the next line at t'oher end. Being early INS it used to 'get lost' with montonous frequency and occasionally picked up its skirts and belted of hundreds of miles into East Germany at a great rate of knots.