air consumption estimation algorithm

[Dirk Hohndel]

On Tue, 2013-10-15 at 19:29 +0200, roberto forini wrote:
> Good evening,
> sorry for my bad english, i'm new to the mailing list and i'm new also
> to subsurface but i apreciate it a lot. Unfortunately i'm unable to
> join your developing team (maybe next year!!) but i would like to
> share a very simple way to estimate the air consumption without the
> exact data from the gas sensors.
> I was thinking if it is possible to estimate the air consumption
> during the dive.During my dives i usually take note about the start
> pressure and final pressure of the tanks (backgas, deco, argon tank
> etc). Subsurface (3.1.1 for windows) only generate a smooth quadratic
> curve from the start pressure to the end pressure of the relative tank
> of all the gas. (see picture 1). 

Actually, no it doesn't. It assumes that you have a constant SAC rate
and then distributes the air consumption over the dive so that it
follows your depth accordingly.

>  I did it only with a simple datasheet calculation and the result is
> the graph in the very right of the picture 2. It gives a quite real
> air consumption curve. In the picture 2 you can see the yellow curve
> that is the linear consumptioni curve, the red curve is the estimation
> and the blue curve is the depth extract from xml file of the dive.
> i've check the estimation many time and works great for me! I know
> that is only a "beauty function" but maybe could be interesting
> compare the estimation with a real curve extract from sensors data.

I think your curve might be the same as ours (except maybe for errors
and/or different assumptions here and there)

/D