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Joined: Aug 2005
I don't have an HP01, but from what I remember it's got a screwed-on back, like many waterproof watches. You can get 'universal' tools for taking the backs off waterproof watches -- the one I have is Swiss, and made by 'Jaxa'. It's adjustable to
fit different size cases, and has interchangeable bits to fit different types of back (and you can buy these bits as spares, and then grind them to fit other case types).
This tool is not cheap, but I've found it very useful for removing locking rings, watch backs, and so on. Maybe it would work on the HP01.
I know where you can buy them in the UK, but that's not much help, I guess.