Ah, explains why I've seen the odd report of a Pilot landing at the wrong airfield. They must have one of these gadgets (gotta have them all, you know. Latest version only, please!)
So presumably the guy who landed at Southampton last year (UK, South coast) when he thought it was Oxford (NW of London, and not a ship in sight...) had a new gadget based on these principles, and had to leave the manual behind as, presumably, that would put him above Max Weight, so mistook variation for deviation, and made an error as a result.
