How do dive computers calculate nitrogen absorbtion and clearance when using nitrox?

[GJC]

Do computers only adjust for nitrox by calculating the EAD and tracking time and depth for that adjustment or are they doing something more complex?

Do they give credit for faster offgassing when using nitrox on ascent and at the safety stop or are they just using air calculations (at EAD) for less accumulation?

I am a nitrox recreational diver so please limit answers to that level.

 

[tursiops]

They use the calculated partial pressure of nitrogen, based on depth, for both ongassing and offgassing calculations. It is the same idea as EAD, but done directly for the percentage nitrogen in the gas rather than starting with 79% (air) and then adjusting for (say) 68% (32% nitrox).

 

[GJC]

And if I dive really shallow (less than 15 feet) with 40% nitrox, my residual nitrogen would be lower than if I had stayed on the surface because the partial pressure of nitrogen during my dive would be lower than air at sea level. Would the computer remember that and carry that over to my next dive?

 

[rsingler]

Yep.
It's all just formulas.
But you're ongassing as soon as you hit the surface. Your slow tissues didn't change much during your shallow dive. Your fast tissues adapted quickly. No problem.

 

[Celt]

If you tied a piece of lead to the computer and lowered it in from the boat would it do the same thing? That’s what I’d like to know?

 

[rongoodman]

If you tied a piece of lead to the computer and lowered it in from the boat would it do the same thing? That’s what I’d like to know?

Except maybe for a couple of recreational computes that attempt to factor in heart rate/skin temp, yes. The only thing it knows is pressure and time, in addition to whatever you've told it regarding the gas mix you're diving.

 

[kmarks]

Someday, maybe, after we all get our government nanobot injections and our computers can connect and monitor the actual conditions of our blood, things will be different. But for now, it's all based on the same science as the dive tables, estimated solely on the depth of your computer and the inputs you give it, such as the %O2/N2 in your mix.

 

[rhwestfall]

Someday, maybe, after we all get our government nanobot injections

hoping they skip over the suppository development scheme...

 

[boulderjohn]

If you tied a piece of lead to the computer and lowered it in from the boat would it do the same thing? That’s what I’d like to know?

It's been done.

I was once on a dive in Cozumel, done on EANx 32, and during the dive the DM realized his computer was set to air. As soon as we ended the dive, he dropped the computer into the water on a line so that it could do the deco stop that would allow him to do the next dive.

 

[broncobowsher]

Not uncommon to surface from a deco dive and have the fast tissues on gassing Nitrogen. One of the cool features of a Shearwater.
First saw it in my rebreather class where we spent a couple hours in a pool on pretty much pure O2.
If you have a Shearwater (or can borrow one) and have a pool with a deep end, set it to 99% O2 and put it at the bottom of the pool for a couple hours. fish it out and look at the tissue loading. It is the inverse of a dive as far as Nitrogen loading goes.