it allows for 2 gas mixing right? this is the only reason why my dive instructor would recommend the amphos over the geo 2 but as i'm doing my research, i read that both allow 2 gas mixes.
Hi there,
I don't think you should worry about the ability to use two separate gasses on a single dive, or on the computer having a gauge mode. Both of those things are in the tech diving realm, and as a new diver, you're likely not doing any technical diving in the near future. When and if you do try tech diving, you will almost certainly want something different regardless of what you get now, unless you get a full-on tech computer like the shearwater petrel. And tech diving has so many other expenses that a computer/bottom timer is not a significant expense in that world. (or doesn't have to be)
Your initial plan of getting something small, simple, and inexpensive is the way to go, IMO. What you need in a computer is depth/time info, NDL, a graphic representation of N2 loading (this is very important, more so than NDL to me), nitrox compatibility, and an ascent rate indicator. It also nice to have a safety stop counter. I'm pretty sure that almost all dive computers have these features.
The reason the N2 loading bar graph is so important is because it gives the best indication of your saturation status at the end of a dive when it's really important to know. You can decide, for example, to stay longer at a safety stop if the bar graph indications that you are near the 'red zone' of mandatory deco. This can help you feel better after diving.
The thing to remember about computers is that they only offer data based on your depth/time. They have no ability to actually monitor your tissue loading, and as such you are best advised (like all divers) to learn whatever you can about DCS, what factors are associated with it, and some basic understanding of how the main deco theories operate. This puts you in control of your dive to a greater extent than following a computer. The PADI encyclopedia of recreational diving has a good chapter that introduces basic deco principles. I'm sure there are other resources. The main thing is that when you dive with more knowledge of how our physiology reacts to breathing compressed air, you can alter your dive behavior. This is the best safety practice.
The differences between the algorithms can seem really daunting, as you could wear two computers on the same dive, and have one telling you your NDL is an hour, while the other might say 5 minutes. That scenario is more likely near the end of a dive when NDL doesn't really matter. But the computers vary greatly in what is called 'offgassing' credit for ascending to shallow depth, and particularly in how the computers express the difference. Again, that N2 loading bar graph can be very useful in this way, because it tends to vary less among the differing algorithms.
Sorry, I haven't been very helpful in recommending a particular computer, I guess because I don't think it matters much. I've had the same aeris atmos for over a decade; it's still working although the backlight is gone and it's getting a little wonky with battery use. I think any of the low price puck computers will work fine. You can spend a lot and really get almost nothing for your money except features that are somewhat useless for normal recreational diving. Some of the newer OLED screens are terrific if you dive in the dark a lot, but they're also pricey. I personally like the more liberal haldanean computers (i.e. oceanic) but I also dive intelligently with a good knowledge of how my dive behavior is likely to affect my post-dive health. Except in cases of multiple deep dives/day like a liveaboard off shore, I'd be perfectly happy diving with a bottom timer and maybe a smart phone app to check dive planning. It's the multiple repetitive dives and aggressive profiles that require more precise calculations, and those dives are inherently riskier regardless of what computer you use.
