2 or 3 gas computer, looking for recommendations

[fire_diver]

I would say it compells you to check if your computer is set according to your mix.

Yes, but I don't agree with setting it to air. The Duo would force you to check gas mixes by setting them to 100% after any nitrox dive. That way, if you didn't set to correct mixes between dives it would very quickly start screaming at you during the next dive when you appeared to violate MOD and/or OTL. putting you at 21% when you might be diving much higher mixes could result in excessive deco times while far exceeding OTL.

 

[doctormike]

Yes, but I don't agree with setting it to air. The Duo would force you to check gas mixes by setting them to 100% after any nitrox dive. That way, if you didn't set to correct mixes between dives it would very quickly start screaming at you during the next dive when you appeared to violate MOD and/or OTL. putting you at 21% when you might be diving much higher mixes could result in excessive deco times while far exceeding OTL.

I agree that having the computer reset to air is somewhat "recreational" in style, but there is some logic to the reasoning behind that design choice. By far the most likely mode of failure is the operator forgetting to match the computer to the mix. This happens all the time. So with an automatic reset to air, the outcome will be a shortened NDL (or a more conservative profile, depending on how you look at it).

Since the NDL is a dynamic thing that changes during the course of a dive, it is something that many people rely on the computer to track (that's one of the main reasons for having a computer in the first place). The MOD, on the other hand, doesn't change, and is determined when you fill the tank. I don't think that many people dive a computer to keep them above the MOD, that would suggest a serious lack of situational awareness. Specifically, it would be a very unusual diver who is Nitrox certified, understands what the MOD is ahead of time, but is relying on a computer to keep him or her above it.

As far as the computer automatically resetting to EAN100, I have never heard of that feature. I'll believe you if you say that the Duo does that, but that seems to be a very odd choice. "Screaming" computers are often not heard through hoods, and many people shut off audible alarms altogether... is the idea that when (not if) you forget to gas match your computer, you are supposed to do that during the dive? A different approach, I suppose...

If you are talking about dives where deco times and OTLs are relevant, then you aren't really talking about recreational diving. I think that most technical divers wouldn't be relying on their computer to given them deco and O2 limit information on the fly. You would have to be doing a lot of recreational diving to approach the OTL on a single dive, let alone far exceeding it, and excessive deco times never hurt anyone as long as you have enough gas, right?

 

[fire_diver]

That's my point though. A multi gas computer with 100% O2 capability is by design, something for outside of recreational use. I would agree with you that for strictly rec divers, breathing EAN with 21% in the computer is only going to help. If you are someone who is rec-tec and using the computer for primary deco times and OTL tracking, then resetting to 21 can be very bad. The idea wasn't to set mix while diving, and in fact, I think that is impossible. The idea was to force an end (at least temporarily) to the dive because you obviously weren't paying attention to all the details you should before splashing. At least, that's the synopsis I remember from the literature.

I'm not going to argue the merits or lack-there-of for computer deco, or the EAN training standards of some dive instructors. Those have been rehashed to death over the years.

 

[tursiops]

I would say it compells you to check if your computer is set according to your mix.

Yes, that's why they force me to do it. But I'd prefer to make that choice myself.

---------- Post added June 30th, 2014 at 12:21 PM ----------

The Duo would force you to check gas mixes by setting them to 100% after any nitrox dive.

Actually, it gave you the choice: you could turn your "FO2 default" to OFF, and it would retain any Nitrox settings until midnight...nice for diving the same mix all day. If you set the default to ON, then after each dive it would default to PO2=99% and PN2=79%...about as conservative as one can get!

I've just reread the TRIO manual. It only allows the FO2 Default to be ON, not OFF, and resets to the 79% N2 and 99% O2 after 12h. So you can do a few dives without resetting the mixes, but not all day/night. At least the display flashes that you are in default; that's nice.

 

[doctormike]

That's my point though. A multi gas computer with 100% O2 capability is by design, something for outside of recreational use. I would agree with you that for strictly rec divers, breathing EAN with 21% in the computer is only going to help. If you are someone who is rec-tec and using the computer for primary deco times and OTL tracking, then resetting to 21 can be very bad. The idea wasn't to set mix while diving, and in fact, I think that is impossible. The idea was to force an end (at least temporarily) to the dive because you obviously weren't paying attention to all the details you should before splashing. At least, that's the synopsis I remember from the literature.

I'm not going to argue the merits or lack-there-of for computer deco, or the EAN training standards of some dive instructors. Those have been rehashed to death over the years.

Yeah, I guess I see your point, but it seems to be an accommodation to a very limited demographic. Specifically, people who (1) use a computer to control their dive profile, (2) forget to gas match and (3) are doing dives with a staged decompression obligation (i.e. technical diving, not sure what the definition of "rec-tec" is but it shouldn't involve staged deco).

As I said, an odd design choice, given that the technical dive training that I have had stresses that all of this is worked out ahead of time, including mixes and profile, and that "flying the computer" without generating, understanding and/or following a predetermined dive plan is frowned on.

Great sig, BTW!

 

[fire_diver]

Actually, it gave you the choice: you could turn your "FO2 default" to OFF, and it would retain any Nitrox settings until midnight...nice for diving the same mix all day. If you set the default to ON, then after each dive it would default to PO2=99% and PN2=79%...about as conservative as one can get!

I've just reread the TRIO manual. It only allows the FO2 Default to be ON, not OFF, and resets to the 79% N2 and 99% O2 after 12h. So you can do a few dives without resetting the mixes, but not all day/night. At least the display flashes that you are in default; that's nice.

Oh yes, that's right, I forgot it changed the PN2 also. I had never changed the FO2 default setting, so I forgot you could turn that off.

(i.e. technical diving, not sure what the definition of "rec-tec" is but it shouldn't involve staged deco).

As I said, an odd design choice, given that the technical dive training that I have had stresses that all of this is worked out ahead of time, including mixes and profile, and that "flying the computer" without generating, understanding and/or following a predetermined dive plan is frowned on.

Great sig, BTW!

Lots of "rec" divers who decide to undertake "tec" on their own and typically fly by the computer.

I agree completely about pre-planned deco profiles with contingency profiles. That's what I was taught also.

 

[doctormike]

after each dive it would default to PO2=99% and PN2=79%

Oh yes, that's right, I forgot it changed the PN2 also. I had never changed the FO2 default setting, so I forgot you could turn that off.

I must be missing something here. Do you mean FiO2 and FiN2 (fractions of inspired O2 and N2 respectively), since we are talking about percentages? How does the computer reset to 99% O2 and 79% N2? What kind of gas is that..?

Lots of "rec" divers who decide to undertake "tec" on their own and typically fly by the computer.

I agree completely about pre-planned deco profiles with contingency profiles. That's what I was taught also.

Right, and that decision is universally panned in technical diving circles. It's hard to believe that a major equipment manufacturer would design around support for such a practice. Maybe I'm missing something here too...

 

[fire_diver]

I must be missing something here. Do you mean FiO2 and FiN2 (fractions of inspired O2 and N2 respectively), since we are talking about percentages? How does the computer reset to 99% O2 and 79% N2? What kind of gas is that..?

It's not. It's the theoretical "gas" that will force your computer into warning mode if you dive but don't reset the gas, thereby ending your dive.

I'm not saying it's the best, or even a "good" idea, just that is what that model of computer did to help ensure divers did their checks. Probably a result of lawyers being involved.

 

[doctormike]

It's not. It's the theoretical "gas" that will force your computer into warning mode if you dive but don't reset the gas, thereby ending your dive.

I'm not saying it's the best, or even a "good" idea, just that is what that model of computer did to help ensure divers did their checks. Probably a result of lawyers being involved.

Hooray! The lawyers have succeeded in overturning Dalton's Law! If we can just find a shop that will fill tanks with that stuff, we can get some REAL bottom time...

 

[txtroop07]

Good to see you back fire_diver! Let me know what you decide on a new computer as my Cobra is no longer trustworthy. And btw, my roommate at FOB Rustamiya was smelly!