Just got nitrox certified :)

[boulderjohn]

Well, air IS nitrox 21%, isn't it?

If I'll be diving nitrox regularly, I'll probably keep my Suunto constantly in nitrox mode (set to 21% if I'm diving air, but that's a non-issue since it reverts to 21% two hours after I've set the percentage) since the display is slightly different in air mode and nitrox mode. I'm a firm believer in having consistent instrument readouts.

Here's the problem with the Suunto reversion system. Let's say you dive 32% and have a nice surface interval. You prepare for the second dive on 32% and check your computer to make sure it is correct. It is. You go to the back of the boat to drop in, at which point it reverts to 21% without your knowledge. Once again, ask Suunto why they think that is a good idea.

 

[Storker]

Here's the problem with the Suunto reversion system. Let's say you dive 32% and have a nice surface interval. You prepare for the second dive on 32% and check your computer to make sure it is correct. It is. You go to the back of the boat to drop in, at which point it reverts to 21% without your knowledge.

Yep, I absolutely see that point. Which is why I've already decided to make setting, not just checking, the percentage a part of my pre-dive check when I'm diving nitrox.

 

[AfterDark]

Thanks BoulderJohn...

Seems the Oceanic Veo 2.0 - Air or single Nitrox mix to 50% O2 - does not allow for multiple gases during SIT time but I need to investigate further...
So there is at least one out there.

I tend to doubt that. I have 2 Oceanic VEO 1 NX PDCs that allows me to change to any % up 50% between dives.

 

[JohnN]

Here's the problem with the Suunto reversion system. Let's say you dive 32% and have a nice surface interval. You prepare for the second dive on 32% and check your computer to make sure it is correct. It is. You go to the back of the boat to drop in, at which point it reverts to 21% without your knowledge. Once again, ask Suunto why they think that is a good idea.

And what model might that be? My Vyper Air stays where I left it, as does my Vytec, as does my old-and-moldy Mosquito

 

[Basking Ridge Diver]

I have read through the entire Operating Manual and it is not explicit that this is how it works... It could very well work that way - and what they mean is you can only use one EAN mix in one dive - aka Dive Air or EAN and not have a secondary gas for the Deco Stop.
But I have never tried the EAN FO2 setting because I never needed it... I will play with that setting once the ice thaws... It does clearly say "1 Nitrox Gas Mix" so I took it at face value.

 

[Storker]

The Stinger seems to retain the value during the SI (p. 45):

If a dive is started within 2 hours Stinger retains this value until the dive series is finished. If unused, the computer will retain the manually entered value for the selected oxygen percentage for about two hours, after which it will revert to the default setting of 21%.

The Zoop seems to retain the value during the SI (p. 28):

Manually entered values for oxygen percentage are retained for about two hours after the setting if a dive series has not started. In case a dive series is started, the set value is retained until a new dive series is started or a new value is entered manually.

The user manual for the Cobra is unclear (p. 70):

If unused, the computer will retain the manually entered value for the selected oxygen percentage for about two hours, after which it will revert to the default setting of 21% O2.

Anyway, it seems that the percentage will be retained during the SI, but will revert to 21% after the no-fly time has expired, or if you don't dive within two hours after setting the percentage for the first dive of the day.

I've probably misunderstood the wording in the Cobra manual when I believed that it reverted to 21% during the SI.

 

[boulderjohn]

And what model might that be? My Vyper Air stays where I left it, as does my Vytec, as does my old-and-moldy Mosquito

My old Cobra did it.

 

[tursiops]

I have read through the entire Operating Manual and it is not explicit that this is how it works... It could very well work that way - and what they mean is you can only use one EAN mix in one dive - aka Dive Air or EAN and not have a secondary gas for the Deco Stop.
But I have never tried the EAN FO2 setting because I never needed it... I will play with that setting once the ice thaws... It does clearly say "1 Nitrox Gas Mix" so I took it at face value.

You are on the right track, which would probably be easier to get on after a Nitrox class!

You set the computer for a gas mix, before a dive. It calculates N2 uptake during that dive, based on your setting. After surfacing, it doesn't matter what the computer was set at, you've now got some N2 in you that shortens your allowable second dive. You set the new Nitrox mix for the second dive before the second dive, and go diving. The computer takes into account the N2 already in you (that is, still remaining after your surface interval), and calculates the new input based on the new Nitrox setting. And so on, for 3rd and 4th etc dives.

Much of the discussion in this thread has been about the small number of computers that do something during the surface interval that is unexpected or weird or otherwise not desirable like reset themselves to air, or reset themselves to some impossible mix like 79% N2 and 50% O2, so all kinds of alarms go off during the second dive because you either viloated an NDL or violated a maximum depth for the 79-50 impossible mixture....but the manufacturers say they are keeping you safe. Balderdash. Many folks are now refusing to purchase comnputers that do that nonsense.

Your Veo allows one nitrox setting at a time, for each dive.....some computers allow 2-3 or more, with the additional setting being available during the dive so you can indeed shift to a different gas for deco, or two different gases for two different deco mixes, etc.