Quote from parabellum:
When based in Germany made a special trip to Düsseldorf to buy the Aristo Aviat in the airport shop, best investment ever. Had a choice of slides, high and slow speed and the rotatable cursor on the front was invaluable. When it came to Flight Planning, Plotting and Nav Gen in the exams it saved many valuable minutes. Useful book of instructions and a nice leather case too!
[Unquote]
Yup, that's the one (see my post above). And for those who can't contemplate anything that isn't based on a digital computer, a hands-on mechanical device to represent the 3 vectors is hard to beat.