Suunto Cobra and Nitrox

I have a Suunto Cobra computer and currently doing a Nitrox course. My question to Suunto was ...if you did your first dive of the day on Nitrox and the second dive of the day on regular air, do you need to change the computer model from Nitrox to Air...OR keep the computer model in Nitrox mode and just set the oxygen% to 21? Suunto replied and said that once in Nitrox mode, the second dive would need to stay in Nitrox mode and the oxygen% changed to 21%.

No other info. was given. It would seem to me that the computer should be capable of switching the model type back and forth, and adjusting everything accordingly. Obviously Nitrox isn't meant for every type/depth of dive. If you are on vacation doing multiple dives on multiple days, and only using Nitrox on a handful of dives, I would think the computer would be able to adjust as opposed to keeping the model in Nitrox mode all week. Obviously it is no big deal to keep the Model in Nitrox and adjust the oxygen accordingly. You need to plan the dive and dive the plan, so checking/setting the computer is just part of the task.

I know as a Nitrox diver, more planning is involved and one should not let the computer do the "thinking" for the diver, but nowhere in the Cobra manual is there a discussion about this topic. I requested more info from Suunto but have not heard anything yet. Is there anyone that has found out more info. on this topic?

You can switch from Air to Nitrox - once - in a diving sequence. You cannot switch back until the computer has cleared itself. Too bad, as the air mode deiplay is far more useful with its CBT.
Rick

Can you clearify "CBT" for me?

Hallmac

CBT stands for Consumed Bottom Time. There is a bar graph in air mode that shows how much No-Deco time is left. It goes from Green to Yellow (with about 10-15 min. of No Deco time left) to Red (O No Deco time left). In the Nitrox Mode this bar graph is replaced with an oxygen toxicity buildup meter.

I did hear back from Suunto and they said that you can start in Air mode and then switch to Nitrox. But after a Nitrox dive, you cannot switch back to Air mode until the No Fly time is met. At this point the computer has a clean slate and then you can switch back to air. So I guess on a vacation, once you use a Nitrox tank, you are going to have to keep it in Nitrox mode until you get home (or jst don't dive as often..but that ain't going to happen).

This happens on the Stinger, too. That's just the way Suunto's interface is set up. It bothered me the first time because it doesn't say "AIR". I don't really see where the problem is, though. You need to adjust your computer before each dive when you dive with Nitrox, anyway. And after a couple of hours (not sure how long), the computer will switch back to EAN21 using the same NDLs as air (since it is...).

I don't really see the problem... if you use say 40% nitrox on one dive and then you decide to use air the next, just fight the brain rot a little and change the nitrox to 21%. It should stay on 21% til you change it or it goes back to air. Either way, you're fine. I guess the Fins figured we knew 21% Nitrox is regular air, right?

Yes, they did, though theirs tends to be colder than most of ours...

I guess I dont understand your question, but isnt 21% the same as AIR anyways??? Or you want the computer to go back into standard AIR mode??? I dont know why they even have AIR mode on a NITROX computer... You can change it from 21 to 50 right??? SO, where's the rub???

which is replaced with the OTU display when you're in Nitrox mode.

Its a non-issue really, because the CBT is just a graphical representation of the numerical NDL value that's always on the screen, and you can call the CBT display anyway with the buttons if you really want to (why would you?)

Just leave it in Nitrox mode and set the FO2 to 21%.

Mine's been in Nitrox mode since the first time I dove Nitrox with it. It does reset itself to 21%, but as far as I can tell, it never automatically resets itself back to AIR mode.

Personally, I'd rather have the OTU meter there than the CBT meter, since, as it's been stated, I can already see my NDL on the screen at all times, but without the OTU meter, there's no (brain rotted) method of seeing this information.