[PATCH] Support different salinity in planner

[Robert Helling]

On 12.11.2014, at 23:33, Anton Lundin <glance at acc.umu.se> wrote:

Anton,

> Depth is often mentioned in a length unit, but what we care about is
> pressure. When diving in fresh water the pressure is lower than the same
> depth in salt water. This adds support for using different salinities in
> planning.

of course I agree that the relation between depth and ambient pressure depends on the density of water and thus on the salinity. 

Of course, I don’t know about you, but I myself don’t take a yard stick to the water but rather used depth gauges (e.g. my dive computer) that pretend to measure depth but in reality measure ambient pressure (and don’t take into account the salinity). So what we call “depth” in diving is, most of the time, actually not really depth but “effective depth” being the pressure equivalent depth assuming some standard diving liquid.

What I am trying to say is: It’s true that it is an error of not taking it into account, but when running a deco schedule against a depth gauge do do this error twice in opposite directions and thus it cancels out. Your patch eliminates this error once, but strictly speaking, the resulting deco profiles should then be measured with a yard strick rather than a pressure based depth gauge, otherwise they are wrong (although probably only by a tiny amount that does not really make a difference). But then the error in the first place was probably not significant. But as a plus, it makes the user believe we take everything into account… ;-)

Best
Robert

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Robert C. Helling     Elite Master Course Theoretical and Mathematical Physics
                      Scientific Coordinator
                      Ludwig Maximilians Universitaet Muenchen, Dept. Physik
                      Phone: +49 89 2180-4523  Theresienstr. 39, rm. B339
                      http://www.atdotde.de

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