Blackwood
Contributor
I believe her point was that the lack of air in an AL80 would decrease their dive time below the NDL. Which may be true, depending on the diver, at least for the first dive of the day.
To be fair, I don't think she was suggesting that just jumping in with an 80 and using it until it's gone is a good plan. She was talking about two divers using one computer, and simply mentioned that gas is generally more constraining than NDL in a post prefaced with "Although I don't think sharing a computer is a practice to be encouraged..."
As you noted, as dives are repeated, "NDL" decreases for a given depth. However, that decrease applies to both divers. So yah, on the 4th or 5th dive, that gas supply may outlast NDL, but it's irrelevant to the concerns of sharing a computer which I personally believe are mitigated by general algorithmic conservatism and, more importantly, buddy proximity. If you are so far away from someone that you have a drastically different inert gas loading, he/she is not your buddy; you're solo. I'm not very concerned with a few feet here or there (in spite of table methodology which would have us conclude that while one guy is A-OK at 79 feet, his buddy is screwed at 81).
That said, I don't encourage it either... it's not my position to encourage or discourage anything.
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