Deco in the information panel not consistent

Robert Helling helling at atdotde.de
Mon Jan 12 01:57:04 PST 2015


Patrick,

> On 12.01.2015, at 09:37, Patrick Valsecchi <patrick at thus.ch> wrote:
> 
> In the attached screenshot, you can see where I had the mouse cursor with hand drawn black cross. There, you can see clearly (with the green and red areas) that the calculated ceiling was 12m and the DC ceiling was 9m.
> 
> But if you look at the Information panel on the right, it shows 2 min at 6m for the calculated deco and 1min at 9m for the DC deco. The calculated ceiling for the 5min tissue is 10m which is consitent with the graph and a calculated ceiling of 12m.
> 
> So why is the calculated Deco information showing "2min @ 6m" when the calculated ceiling is 12m?


these values are calculated in profile.c around line 860.

I agree these data seem to be contradictory but in fact they aren’t if you take into account what they actually mean:

By “ceiling” we mean the minimal depth that (according to the model) would support the current inert gas loadings of the diver’s body.

The difference to the stop depth comes about as the diver does not instantaneously pop to the ceiling depth but we take a finite ascent rate into account. During that ascent, some of the tissues will already desaturate which can move the ceiling upwards so that at the time when the diver reaches the old ceiling depth it has moved up. In particular with the 3m/10ft quantization of stop depths that can have a significant effect.

In your example, the true (unquantized) ceiling is at 10m, so it does not have to move much to make 9m rather than 12m the first stop depth.

Does that help?

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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