O2 percentage - round up, round down?

[Chugwhump]

Flip a coin.
Go by your mood.
Very few dive shops have an O2 meter that is consistently on the button at half a percentage point anyway.
And very few individuals either (at least here in SoFla).

I certainly buy into the round up for depth/mod consideration, round down for time/deco concept as others have stated.

Chug
Holds back 10% as a general rule.

 

[Dr. Lecter]

I round up for mod calculation and round down for computer entry.

This, but bear in mind that the CNS% reported by the computer will be less conservative (not that it really matters given how inexact CNS loading is anyway).

 

[Bigd2722]

I just feel like there's too much worrying about minor things in diving, when major issues are overlooked (are you able to give air ANYTIME to your buddy without him having to come and grab you? are you able to deal with a stuck inflator in whatever position at any time? etc.)

While I wholeheartedly agree with your position, this is a fun discussion for the nerds. I had this same discussion a couple of years ago on another board. It did not get nearly as much technical input/information as this discussion