Salinity vs. density of water

[Robert Helling]

Hi,

for those of you who do not follow the discussion in the google forum:

A user reported a wrongly calculated SAC in https://groups.google.com/d/msgid/subsurface-divelog/583da598-2554-4309-9387-a150e47997fd%40googlegroups.com <https://groups.google.com/d/msgid/subsurface-divelog/583da598-2554-4309-9387-a150e47997fd%40googlegroups.com?utm_medium=email&utm_source=footer> and I could track it down to a line in the xml file that specifies the salinity to 35g/l. But salinity value in subsurface is actually treated as the density of water (in the conversion of depth to ambient pressure) and the UI only displays this value but there is no way to set it manually (outside the planner). So my guess is it came from the dive computer which happens to be an Oceanic Oci 279.

My question is: what is the semantic of the salinity in libdivecomputer, is it “just the mass of salt per liter of water” (in which case we would need to change the translation in subsurface) or is it like in subsurface the density of water (i.e. mass of water plus salt per liter)? In the latter case, there needs to be a conversion when reading out this oceanic computer.

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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