Graph documentation [was: Re: Meaning of GF settings]

Robert C. Helling helling at
Thu Jan 10 15:02:56 PST 2013

On Jan 10, 2013, at 6:08 PM, Dirk Hohndel wrote:

> I hear you. I learned FORTRAN in high school and forgot it as quickly as
> I could. I actually looked at those same sources before Heinrichs and
> Weikamp kindly offered to let me start from their C sources…

You mean you have a VPM implementation that is more readable than the original FORTRAN code? That would be interesting to see.

  I was simply wondering if this would be something
> that long term you'd be interested to play with.

That is quite a precise description of the situation.

> But what I like about VPM(B) and RGBM is the abstract idea behind it. To
> me it feels more "right" to try to estimate the bubble build-up then to
> use some magic formulas to make 16 (or fewer in many cases) compartments
> that simulate my tissues match empirical data. Call that naive (because
> frankly, I realize it is), but I would love a working, well tested
> bubble model :-)

My understanding is you have the bubbles in addition to the 16 compartments. You first compute tissue loadings for the compartments just like Buehlmann. Then only as a second step you don't calculate M-values (or their GF corrected version) but you pretend these compartments now feed their inert gases to bubbles. 

> Having said that - questions about this keep coming up and allowing
> people to play with this in the rather nice visual representation that
> Subsurface can do - and do so on top of their own dive profiles... I
> think that does have value.

I would love to do that myself.

> I certainly have spent way more time than I'm willing to openly admit
> using different GFlow/high pairs against my existing deco dives... :-)

That's exactly what you are supposed to do. I did the same (feature request: It would be great to have sliders for the GF's rather than having to type numbers). I realized only quite late that even though the green area changes a lot when you play with GF_low so the effect seems huge it is not since the ceiling only indicates the first stop and that typically is quite short so if you ascent slow enough you don't do a stop at all. You have to look at the full decompression profile so see how significant the effect is (like total time to surface).


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