Diving Nitrox with Computers?

[driebel]

Hi everyone,

I've been diving for a few years now, but mostly as a "tourist" diver, only on vacations. I'm now looking to get more serious and consistent with my diving, and have therefore just invested in my own gear, including a dive computer (Suunto Vyper). I did my first EANx dive with said computer over the weekend, and I noticed that while diving with nitrox, the computer displays my current depth, max depth, O2 percentage, no decompression time remaining, and running dive time.

My question is, why the max depth and/or O2 percentage displays? To me, while diving with EANx, it would be most useful to have a large reminder on my wrist of the MOD for my mix, rather than say, the actual percentage or the max depth attained during this dive. If I were designing the computer, I would have replaced at least one of those (probably the percentage) with the MOD. My thought is that a note saying "hey dummy, don't go below this depth!" is more useful in real time than a note reminding me what specific percentage I'm diving with.

Can someone more experienced tell me why this is a more useful piece of data?

Cheers,
Dave

 

[Hemlon]

A Nitrox-compatible computer will do all of the calculations with the parameters you enter.

 

[oly5050user]

Hi everyone,

I've been diving for a few years now, but mostly as a "tourist" diver, only on vacations. I'm now looking to get more serious and consistent with my diving, and have therefore just invested in my own gear, including a dive computer (Suunto Vyper). I did my first EANx dive with said computer over the weekend, and I noticed that while diving with nitrox, the computer displays my current depth, max depth, O2 percentage, no decompression time remaining, and running dive time.

My question is, why the max depth and/or O2 percentage displays? To me, while diving with EANx, it would be most useful to have a large reminder on my wrist of the MOD for my mix, rather than say, the actual percentage or the max depth attained during this dive. If I were designing the computer, I would have replaced at least one of those (probably the percentage) with the MOD. My thought is that a note saying "hey dummy, don't go below this depth!" is more useful in real time than a note reminding me what specific percentage I'm diving with.

Can someone more experienced tell me why this is a more useful piece of data?

Cheers,
Dave

Much of what you ask should have been covered in your nitrox class.
You MUST keep track of O2 exposure , need max depth to keep within MOD. MOD is usually displayed during plan mode after you enter your % of O2. Many computers have an alarm that can be set to avoid going over max depth.

 

[DevonDiver]

Your computer tracks real time information. The MOD is a static and known before the dive, so common sense probably influenced the designers to de-prioritize this from the in-dive display information.

The cumulative percentage of oxygen exposure is critical information. If you did multiple dives, with rich mixes, then your daily OTUs could easily be exceeded. Most recreational divers won't do this, but it is still essential info - just in case you did.

Obviously, as a responsible nitrox user,.. you will be analyising your mix, calculating your MOD from that analysis and marking your tank with the MOD before the dive anyway. You can set the max PPo2 (1.4 for most agencies) so that it provides an alarm function if you exceed it.

If you really need a visual reminder of your MOD during the dive, just buy a sharpie pen and write it on the back of your hand?!?

 

[fire_diver]

Have you read the instructions yet?

 

[CardShark]

Hi everyone,

>>> I noticed that while diving with nitrox, the computer displays my current depth, max depth, O2 percentage, no decompression time remaining, and running dive time.

My question is, why the max depth and/or O2 percentage displays? To me, while diving with EANx, it would be most useful to have a large reminder on my wrist of the MOD for my mix, rather than say, the actual percentage or the max depth attained during this dive. If I were designing the computer, I would have replaced at least one of those (probably the percentage) with the MOD. My thought is that a note saying "hey dummy, don't go below this depth!" is more useful in real time than a note reminding me what specific percentage I'm diving with.

Can someone more experienced tell me why this is a more useful piece of data?

Cheers,
Dave

Hey, Dave,

As your personal decision of allowable ppO2 at a given level of exertion is what you need to base your judgement of MOD on, the information on your wrist really is giving your brain the needed input.
( Also, if you specify the mix for the dive's maximum potential depth, hitting the sand won't take you past the mix's MOD. )
The Vyper does have a "max. depth alarm" that you could select ( in the place of a MOD display) ; that would replace the process. Hope this helps..

 

[driebel]

Much of what you ask should have been covered in your nitrox class.
You MUST keep track of O2 exposure , need max depth to keep within MOD. MOD is usually displayed during plan mode after you enter your % of O2. Many computers have an alarm that can be set to avoid going over max depth.

Hmmm, let me try to clarify my question. When doing your dive planning the night before, you take note of the MOD and construct a dive plan that keeps you well away from it. I'd personally set a max depth alarm ~3-4m above the MOD to serve as that "hey dummy" reminder, and my intended dive plan wouldn't come close to the MOD.

Assume the user has screwed up and forgotten the plan. Isn't the MOD the more important reminder? What are the advantages (to that user), during the dive, of the O2 percentage over the MOD? Max depth will let you know if you exceeded MOD 10 minutes ago, but by itself, doesn't help you avoid doing so in the first place. There's an audible alarm that kicks in at MOD, but a good design helps the user avoid alarms entirely.

I'm not saying the computer is insufficient for nitrox diving, just wondering what, in a poor-planning scenario (shoot, was that MOD 25 or 35 m?), why is it more useful to be reminded of your mix during the dive, instead of the MOD?

I'm not asking "how do I use my computer for nitrox?," but rather "why is this piece of information (percentage) more useful than another (MOD) during the dive?" My thought is that the mix is useful for the planning, and the MOD is useful during the dive. Suunto feels differently.

Thanks for the responses,
Dave

 

[driebel]

Have you read the instructions yet?

Yep. They didn't go into design philosophy such as "Why we feel this information is more useful than other information."

C'mon, man. The description of this forum specifically states: "This forum has special rules. This forum is intended to be a very friendly, "flame free zone" where divers of any skill level may ask questions about basic scuba topics without fear of being accosted." (Emphasis added)

My question doesn't come close to "I'm dumb and can't use my computer." It's a question about the usefulness of certain information to maximizing safety and making things idiot-proof. I have an opinion of what information is more useful in certain situations, and I wonder why others (the designers) feel other information is more useful.

Your snark isn't helpful.

 

[syntaxerrorsix]

Your dive plan should cover your maximum operating depth. If you are flying your computer instead of the plan you aren't playing by the rules taught in your OW class or Nitrox Course.

The computer relays your pO2 so that you can make an educated assessment of current conditions and adjust your pO2 on the fly (current, cold what have you.)

If you just want a constant reminder of your plan you should use a slate. Your MOD can be anything you want it to be based on your desired pO2. Some folks like a 1.4 some build in conservatism and run a 1.2 most agencies have a 1.6 cut off.

 

[jmasin]

I agree with the others that MOD is a fixed number based on assumptions and your mix, so that's probably why designers didn't feel the need to take up display space with it (makes sense to me anyway).

You mention planning a dive but then not remembering or not diving to plan (i.e. needing the MOD reminder). To me a computer isn't really a reminder of a plan, but real time tracking of the situation against a plan that should be in your head.

My computer (Aeris Manta) is simple, but nice in that on Nitrox it will keep track of O2 and N loading and display/report whichever becomes the limiting factor. As I'm normally well away from MOD, it is almost exclusively the N2 loading which it displays. Of course I can always toggle between them by pushing buttons...

I always dive 32% when I dive enriched, and always use a PO2 of 1.4 as my limit, so I have 110ft pretty well memorized, so I don't need my computer to remind me of that.

Maybe just personal opinions/preferences...shrug.