Because, well you know, I sometimes use it for other stuff that I think is more important [than ultraconservative max 02 settings that can be safely ignored], such as NDL limits, gas supply remaining, elapsed dive time, depth, ascent rate, that sort of thing.
Why did I ignore my computers 02 alarms given that both of my computers and my buddies computer all indicated violations?
Because it just didn't seem right. Because we were at about 60' at the time. Because I didn't think our dive profiles were all that much different than dives I've done 100s of times before. That's all I got..
Although it was a somewhat impulsive decision it appears to have been the correct one given the information provided on this thread primarily by
@scubadada.
I wouldn't go so far as to say it was the correct decision.
As it turns out, your CNS O2 exposure was likely within limits of different methodology than your computer was using, but you had no way of knowing that at the time because unlike Scubadada, you didn't have another computer you knew was running that calculation. All you knew were three dive computers all were telling you to end the dive.
Scubadada is making an informed decision between two computers running different calculations, one more liberal that the other -- but it was a known calculation, he knows he's within limits on at least one of them and he knows why they differ and what that means. Your choice was between computers you knew were telling you to quit for reasons you didn't fully understand and....the unknown.
Not trying to beat you up, but IMHO, that wasn't a very prudent thing to do. It might be a reasonable thing, going forward, to decide which methodology you believe is best and buy a computer that implements it, but if you don't have it with you, or you aren't calculating CNS halftimes yourself (which is not hard), then best practice is to follow the computer. If I ignore my NDL limits on my computer and find out, only after the fact, that I was within limits using some other algorithm, it doesn't make my decision in the moment a good one. It just means that I was lucky.
Past practice is a fallable guide. CNS hits, like DCS hits aren't that reliably predicted. It's sort of like how many bullets to put in the gun before playing roulette. Plus, unless you were using a different computer, then the fact that it didn't alarm on all your previous trips, and did here, suggests that you were diving more aggressively. And, while I haven't done the calculation, you may have been at or even above recommended whole body limits on the days with a ton of dives, which could have been problematic had you had a DCS hit and needed treatment in a chamber.
Kudos for coming on the board to figure all this out. I guess my one piece of advice, which of course you can take or leave, is that there's always another dive. If my computers were hollering at me to turn the dive, and I wasn't 100% confident that I could safely ignore them, I'd turn the dive and figure it out on the surface.
