Change water type

[tormento]

Awesome explanation and great diving computer knowledge, thanks!

I asked as I have interest in physiology and I do my best to know how
things work under the water and inside body.

Your reasons are more than good for the average user.

Il giorno dom 15 apr 2018 alle 20:55 Linus Torvalds <
torvalds at linux-foundation.org> ha scritto:

> On Sun, Apr 15, 2018 at 12:07 AM, tormento <turment at gmail.com> wrote:
> >
> > Henry's Law is based on (partial) pressures and not depths. I dunno how
> > diving computer talks to subsurface. If giving depths instead of
> pressures
> > it would be a pity.
>
> Almost all dive computers only give depth.
>
> Some give salinity, some don't. And some only give the flag (sweet vs
> salt) rather than the salinity value they actually use to calculate
> depth.
>
> In other words: do not EVER play games with salinity. You don't know
> what it was, and you will get it wrong.
>
> The whole notion of "user should set salinity" is broken garbage. A
> dive computer shouldn't even have that setting. Because that setting
> cannot possibly matter, because the only thing that matters - and the
> only thing the dive computer measures - is actual pressure, and all
> you can do with salinity is make a "correction" to the depth
> calculation that you can get wrong.
>
> So in my not-so-humble opinion, a dive computer should always just
> show depth as "salt water equivalent depth", with no way to screw up,
> and no complications. If you dive in a lake, you'll get the depth
> wrong by a few percent, but nobody cares since it's not a really
> meaningful value anyway, it's just a user-friendly approximation for
> the value that matters: pressure.
>
> Giving the users just the absolute ambient water pressure migth be
> *technically* the right thing to do, but it's such a user-hostile
> datapoint that it's completely wrongheaded. It only moves the
> possibility for error into another place (ie the UI during diving, or
> the UI during later logging).
>
> So what you should do is:
>
>  - set your dive computer to salt water (if it has a setting), and
> forget about it. Don't ever touch the setting, all it can do is cause
> confusion.
>
>  - think of "depth" as "equivalent depth in salt water" and be happy
>
>  - mark your lake dives as such in the dive log tags if you care, the
> same way you mark boat dives and buddy names.
>
> The sweet-vs-salt water thing has absolutely zero meaning outside of
> informing yourself, and has exactly the same relevance as the name of
> your dive buddy: nice to know, but not relevant for any other meaning.
> Don't give it any relevance that will only confuse you and get things
> wrong.
>
> Because anything else is just a disaster waiting to happen. You *will*
> get it wrong, and you will only confuse yourself. Trying to correct
> things later is just going to make things worse.
>
>                     Linus
>
> PS. Yes, there are dive computers that don't report depth at all, and
> report the actual hydrostatic pressure that their sensor gives. Before
> you say "that's what everybody should do", let me just say that (a)
> they are a tiny minority and (b) even they aren't consistent (ie is it
> absolute pressure, or relative to surface pressure?)
>
> So subsurface logs what the vast majority of dive computers give you:
> depth. In fact, we don't even see the pressure, because the conversion
> will have been done by libdivecomputer. So as far as we're concerned,
> no dive computer gives us pressure, but technically you can get the
> water pressure from the Atomic Aquatics Cobatl, from the
> Heinrichs-Weicamp OSTC and from the Reefnet Sensus Ultra. (That last
> one isn't actually a dive computer, it's just a data logging device.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.subsurface-divelog.org/pipermail/subsurface/attachments/20180415/bb515ccd/attachment.html>