[bang-on]

For the sort of diving I'm doing (30m to 40m with not much deco) then I think that back-up computers are overkill. Of course I would like one, but I don't think they're by any means a neccesity.

you would still need depth/time info!

I think the big advantage of backup dive computers (for me) is when you're on a weeks holiday somewhere and one goes wrong and you don't want to wait 24 hours before diving again.

if your dive has gone wrong to point of your dive computer locking you out for 24hours your probably better of not diving for the 24hours.

cheers
barrie