But the computer can't anticipate. You may be at 80' now and running out of Remaining Dive Time for either air pressure, NDL or oxygen accumulation (Nitrox). But YOU know that you are headed for 30' to cruise the reef. RDT based on air pressure may be meaningless. YOU know your rate of consumption will soon decrease dramatically. The computer can't anticipate that. So, the display based on air pressure isn't useful. It isn't your Remaining Dive Time or anywhere close to it. In that regard, the RDT based on NDL isn't accurate either (on ANY computer). About the only thing that is accurate is oxygen accumulation.
It is true that the computer can't anticipate planned moves to shallower or deeper water. But anyone who actually uses an AI computer learns that right away, learns that the RDT essentially means "RDT at your current depth".
So let's take your example (which is a good one): If I'm at 80' and my computer is showing a "safe time" of five minutes, then sure, I know that, within that five minutes, if I ascend to 30', I will have AT LEAST five minutes, and probably more (or conversely, if I went deeper, I would have less time). In fact, I know that almost as soon as I ascend to 30' my computer will recalculate my remaining safe time for me based on all available factors: my current gas consumption rates, N2/O2 saturation, preset reserve pressure, time for safety stop, etc.
Using the same example, if I really ran my AI computer down to zero "safe time" at the 80' depth, that means that either 1) I now have just enough gas to ascend, do a safety stop, and surface with whatever my pre-programmed reserve is, or 2) I am running up against my N2 or O2 limits. Either way, I'm not going to have much if any time for cruising that reef at 30'.
Yes it's true you can't actually turn off your brain when using an AI computer. But pretty much the only thing you still need to know is that any positive safe time will decrease if you descend, or likely increase if you ascend. Zero safe time is pretty much just that, regardless of depth, and you need to be moving on up. Very simple.
And simple is good - you know, the KISS principle. This is something that I think backfires with the "stick to gauges" crowd - you can't argue that AND argue for a "simpler" setup. Because an air-integrated computer is just plain simpler to use.
Some people still like manual transmissions. I have no idea why, but they do, and maybe they deride those of us using automatics as too dependent on technology. I remember when the FCC created a new HAM radio license that did not require knowledge of Morse code, mostly so the packet radio guys could get up and running - who didn't need Morse at all - and they were given a hard time by the old schoolers. People thought pocket calculators would ruin everyone's understanding of math. I'm sure there are those who think the GPS has made everybody brain-dead and that everything would be so much simpler if we all went around carrying just a sextant and compass (and indeed there have been some well-publicized examples of folks driving their cars into lakes because their GPS said to turn - but they're the Darwin Award candidates anyway). There's an entire religious community that feels all this gosh-darned motor-driven stuff is just too out of hand and consciously refuse to move technologically beyond the horse and buggy.
It's a free country - you can be a Luddite if you want. But most of us really appreciate the way well-designed technology takes care of a lot of the details so we can focus our organic brains on more interesting things, and for me - and I'm guessing lots of GPS users - that applies to my dive computer as well.
>*< Fritz
