Make water salinity editable

[Dirk Hohndel]

I recall many, many threads on this mailing list that point out that editing salinity isn't really useful.
At least when diving with a dive computer you are almost CERTAIN to make things worse by doing so. Your dive computer records pressure, not depth.

I won't try to rehash all of these discussions here, just point out that I wonder if this is a good direction to go.

/D

> On May 17, 2019, at 4:12 AM, Willem Ferguson <willemferguson at zoology.up.ac.za> wrote:
> 
> I have code to make the salinity editable on the Information tab. See attached two screenshots. The motivation is twofold:
> 
> 1) Frequently the salinity is not provided when logging a dive. There can be two reasons:
> 
>         a) Either the dive computer does not report on salinity or libdivecomputer does not know how to extract that information.
> 
>         b) The dive is entered by hand.
> 
> 2) To make the salinity datum more immediately user friendly. Most users do not know the density of the water they dive and, in the end, it is treated as one of the main categories of water: fresh/sea/EN13319. For any user it is not intuitive to provide a water density. My current code is backwards-compatible and does not affect the dive or dc structures or the way any of the calculations are done.
> 
> However, there are few issues to be decided on.
> 
> 1) The density of sea water is not standardised. My Galileo reports a sea water density of 1025 g/l because this is what the libdivecomputer parser provides. However, in the rest of the software, as far as I can see, sea water density is 1030 g/l because that is the value of SEAWATER_SALINITY in units.h. We should probably move towards more consistency in this. As far as I can see it does not affect the computations at all but it is not ideal, especially with data where no explicit water density measurements were taken but where the dives only indicates a category.
> 
> 2) I am undecided about the utility of EN13319. This is a European standard for the certification of dive computers, using a water density of 1.0198 for calibrating dc depth sensors. This standard density is used to make the calibration of depth sensors across dive computers comparable. I have not found out why the chose this specific density. The utility of the EN13319 water density is questionable for divers that log dives after a dive. The numeric value is pretty close to the density of sea water (some authorities quote the density of sea water as low as 1.023, less than a half a percent different from that of EN13319. I do not think that EN13319 is a halfway-value between sea water and fresh water. Although the use of EN13319 is likely to be confusing to divers and it clutters the UI, I actually have no strong opinion on this.
> 
> Kind regards,
> 
> willem
> 
> 
> 
> 
> 
> 
> 
> -- 
> This message and attachments are subject to a disclaimer.
> 
> Please refer to 
> http://upnet.up.ac.za/services/it/documentation/docs/004167.pdf <http://upnet.up.ac.za/services/it/documentation/docs/004167.pdf> for
> full details.
> _______________________________________________
> subsurface mailing list
> subsurface at subsurface-divelog.org
> http://lists.subsurface-divelog.org/cgi-bin/mailman/listinfo/subsurface

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.subsurface-divelog.org/pipermail/subsurface/attachments/20190517/68cd9a38/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: salinity1.jpg
Type: image/jpeg
Size: 2725 bytes
Desc: not available
URL: <http://lists.subsurface-divelog.org/pipermail/subsurface/attachments/20190517/68cd9a38/attachment-0002.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: salinity2.jpg
Type: image/jpeg
Size: 5324 bytes
Desc: not available
URL: <http://lists.subsurface-divelog.org/pipermail/subsurface/attachments/20190517/68cd9a38/attachment-0003.jpg>