I do plan to keep it, but you never know... Might get a trading offer for for a Rolex Submariner, than I would have to accept... lolNever saw the F-12 before -- nice minimalist design. Kind of curious why CASIO put such bold attention to the model numbers on watches like the F-12 and F-91W. I'd expect them to be in very small font and off in a corner, muted. Anyway, obscure vintage CASIO watches are very hard to value, as there's often no feasible market sales history by which to judge them. eBay seems to be the defacto sales place. You could post it on eBay with a moderately high BIN price and see if you get any nibbles (inquiries). Yet, it sounds like you want to keep it since you say it's a joy of your collection. My impression is that you wouldn't get a lot money for it (e.g. 50 quid), because it's easy to mistake for a current CASIO. Keep it!