Salinity vs. density of water

[Jef Driesen]

On 2016-02-26 13:45, Robert Helling wrote:
> 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
> [1] 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.

It's the density of the water (in kg/m^3 or g/l). So the same as in 
subsurface.

If the user has an Oceanic OCi, then the value didn't came from there. 
The oceanic backends only supports the salinity field for the VTX and 
300CS. And for those models it only reports the fresh/salt water flag 
without a density value.

Jef