Gee, John, why stop with heart rate readings. For another few thousand EURO on the price tag, I'm sure someone can figure out a way to throw in real-time Doppler arterial microbubble count, real-time blood pressure and EKG, and (while we're at it) why not run a catheter to pick up blood sugar and anything else we don't want to see in the urine. And why not mate the whole thing with an underwater blackberry, an underwater ipod, and an XBox, so we can surf the net, check stock prices and email, download YouTube videos and listen to crap music, and play great games too. What about GPS? Come to think of it, though, with all those great toys on my wrist, why would I want to bother diving?
What's with the gadgetry? OK, I have an exercise watch and chest band that I use (not enough), but when I'm underwater, I really don't l want to let my heartrate get up into the optimum zone for cardio aerobic conditioning. I don't know about you, but when I've beenpushing my housing up-current for four or five minutes, I don't really need a computer read-out to tell me that my heart rate is starting to get up there.
I have a wrist compass too, the kind with a magnetised needle floating in Karo syrup (glycerine? mineral oil?). It points north 24/7, and the batteries never run out. How much would the quality of my life improve if I junked it and bought a D9 with selectable electronic compass function?
Do people really find it that difficult to read their breathing gas pressure on an (analog) gauge? On my last liveaboard trip, there were two or three people with wireless computers. Every dive it was the same thing as they went through the ritual of opening tank valves and synching their wrist computers to the tank transmitters, making sure they weren't locking on to the same channel or something. One of the two divers is a wetpixel guru (no names, of course), so naturally he had a hose analog backup gauge on his rig, so it was no problem when his tank transmitter/computer link tanked, as they always seem to do. The other guy (a Brand-X diver) didn't think he needed a backup analog gauge. Naturally, he ended up missing a dive when his transmitter wouldn't synch one morning, and had to borrow one of my spare SPGs to finish the trip.
As Stephen Colbert might put it, today's word is (or should be) "simplify". That doesn't mean consolidating as many life support functions as possible into one overly complex, vulnerable piece of electronic equipment. Computers are very good at tracking depth, time and calculating nitrogen and O2 exposure. Compasses are good at pointing north, and SPGs are good at reading tank pressure. Compasses and SPGs tend to be more reliable than any computer I've ever owned.
Me, I carry two computers on every dive. Neither is a D9.