[PATCH 2/2] Add initial rudimentary no-fly time calculation

[Robert C. Helling]

On Fri, 8 Feb 2013, Linus Torvalds wrote:

Linus,

> Robert, Jan, could you please give this a look from the theoretical
> standpoint.. The code is pretty straightforward, and it actually all makes
> sense, and even the numbers make sense.
>
> But the numbers - while making sense - are *so* totally not what the dive
> computers report. Some dive computers will give 24-hour no-fly times after
> every single dive, but using actual Buhlmann calculations makes most
> common recreational dives have no no-fly time at all, or very short times.
>
> Sure, I can trigger 12-hour no-fly times with this: repeated dives will
> certainly do it. But even then it's much less than my Suunto will give me,
> for example. Now, Suunto's are known to be crazy about things like this,
> but I'd still like some deco people to take a second and third look. Ok?

After briefly staring at the patch I can say it looks good to me. But I 
have two questions:

1) It is not clear to me what the reference pressure really should be, I 
find http://en.wikipedia.org/wiki/Cabin_pressurization not too helpful: 
When they express it as an altitude, what do they assume about temperature 
(always 15 degrees or dropping by some amount (0.0065 K) per meter? Also, 
shall we protect against usual cabin pressure or shall we actually protect 
against pressure drop in an emergency of the plane (in that case I presume 
oxygen masks help the average passenger sufficiently against hyoxia but 
not divers against inert gas forming bubbles at sudden drop of pressure). 
But I don't know if this makes any relevant difference.

2) I am not sure, the whole gradient factor thing makes any sense at 
altitude: GF_high is supposed to be applied at the surface (and that's 
what is in the formulas) but when you extrapolate to even lower pressures, 
you get effective gradient factors that are even higher (possibly above 
100%). To be safe on that side, I would use GF_low=GF_high=whatever to 
make the depth/ambient pressure dependence of the gradient factor go away. 
But I have no good intuition about what a reasonable GF at altitude would 
be.

Execture summary: I have no clue.

Best
Robert

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Robert C. Helling     Elite Master Course Theoretical and Mathematical Physics
                       Scientific Coordinator
 		      Ludwig Maximilians Universitaet Muenchen, Dept. Physik
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