Salinity

[Anonymous User]

What Salinity/Density does the OSTC assume in calculating depth (i.e. EN13319, 1025...)?

[heinrichsweikamp]

Hello,

The OSTC displays 1Bar=10m, so we are close to 20°C fresh water.

regards,
Matthias

[Anonymous User]

Why not code it to salt water?

[Vincent Kessler]

I am also interested in increasing the precision of the shown depth. Maybe i will take a look at the code and add salinity setting.

Regards,

Vincent

[heinrichsweikamp]

We'll add a salinity setting for the pressure readings in the future (Select between 1.000 kg/l and 1.030 kg/l). For the physiological calculations the ambient pressure is relevant, not the shown depth.

Regards,
Matthias

[Anonymous User]

heinrichsweikamp Wrote:
-------------------------------------------------------
> For the physiological
> calculations the ambient pressure is relevant, not
> the shown depth.
>
> Regards,
> Matthias


Is that true also for Gauge mode and/or when using bail-out tables as primary deco?

The other advantage of a salintiy setting is that Primary and Secondary computer can be aligned to the same salinity setting and it is also more accurate for cave surveying.

[heinrichsweikamp]

OSTCfan Wrote:
> Is that true also for Gauge mode and/or when using
> bail-out tables as primary deco?

The OSTC does not apply salinity factors to the depth reading in any mode (right now).

There are deco tables with salinity factors?

regards,
Matthias

[Anonymous User]

heinrichsweikamp Wrote:
-------------------------------------------------------
> OSTCfan Wrote:
> > Is that true also for Gauge mode and/or when
> using
> > bail-out tables as primary deco?
>
> The OSTC does not apply salinity factors to the
> depth reading in any mode (right now).
>
> There are deco tables with salinity factors?
>
> regards,
> Matthias

Deco tables are based on depth and time... so depth displayed by the computer should be consistent with depth used to produce the deco table.

If safety margins are built in (mine tend to be largish), I do not think the discrepancy makes any difference. However, conceptually, I think the two should be aligned and use the same or similar assumptions.

[heinrichsweikamp]

Hello,

We talking about differences of 1-3% here. Can you tell if your deco table is based on a specific salinity?

There are numberless other factors with much more effect (e.g. workload) that are not included at all.

Regards,
Matthias

[Vincent Kessler]

heinrichsweikamp Wrote:
-------------------------------------------------------
> Hello,
>
> We talking about differences of 1-3% here. Can you
> tell if your deco table is based on a specific
> salinity?
>
> There are numberless other factors with much more
> effect (e.g. workload) that are not included at
> all.
>
> Regards,
> Matthias

Errors add up. I think its always a good idea to keep each single error as small as possible.

Regards, Vincent

[Anonymous User]

OSTCfan Wrote:
-------------------------------------------------------
> heinrichsweikamp Wrote:
> --------------------------------------------------
> -----
> > OSTCfan Wrote:
> > > Is that true also for Gauge mode and/or when
> > using
> > > bail-out tables as primary deco?
> >
> > The OSTC does not apply salinity factors to the
> > depth reading in any mode (right now).
> >
> > There are deco tables with salinity factors?
> >
> > regards,
> > Matthias
>
> Deco tables are based on depth and time... so
> depth displayed by the computer should be
> consistent with depth used to produce the deco
> table.
>
> If safety margins are built in (mine tend to be
> largish), I do not think the discrepancy makes any
> difference. However, conceptually, I think the two
> should be aligned and use the same or similar
> assumptions.

The Deco software I use has a choice of Fresh or Salt water for churning out deco tables.

I am not going to ask the programmer which salinity he adopted for salt water, but I'd guess is medium.

By all means it is not critical, but a choice of salintiy would be good to have on the OSTC. If no choice is given, my preference would be salt water rather than fresh water.

[Bradipo]

OSTCfan Wrote:
> If no
> choice is given, my preference would be salt water
> rather than fresh water.

Why? Wouldn't it be more conservative (i.e. display a greater depth than real) if set for fresh water when diving in salt water? This assuming that you are using the computer only as a gauge and cutting your tables for the correct environment.
Or is it because you dive more often in salt water?

Sorry for the silly question, this is just for chatting. In real terms I don't think this issue makes any difference when dealing with safety.

[Anonymous User]

Bradipo Wrote:
-------------------------------------------------------
> OSTCfan Wrote:
> > If no
> > choice is given, my preference would be salt
> water
> > rather than fresh water.
>
> Why? Wouldn't it be more conservative (i.e.
> display a greater depth than real) if set for
> fresh water when diving in salt water? This
> assuming that you are using the computer only as a
> gauge and cutting your tables for the correct
> environment.
> Or is it because you dive more often in salt
> water?
>
> Sorry for the silly question, this is just for
> chatting. In real terms I don't think this issue
> makes any difference when dealing with safety.


I already build a margin (hopefully substantial) in the tables I cut. From the instruments I would prefer accuracy (also for surveying) and instruments which match one another.

I dive mostly in salt water (in some cases the first 6 meters may be fresh, then brackish, but thereafter salt), so my preference for salt, but I'd rather be able to chose between salt and fresh should I ever dive fresh.

[heinrichsweikamp]

Hello,

I'm just adding the salinity settings to the "Setup Menu". I would say four settings with 1.000kg/l (fresh water), 1.010kg/l (Baltic sea), 1.020kg/l (Ocean) and 1.030kg/l (Med. Sea) is fine, ok?

Salinity can vary even in the same sea a lot (+/- 2%).

regards,
Matthias

[heinrichsweikamp]

Hello,

We just uploaded the 1.33, it has four different salinity settings.

1.33 Beta

Regards,
Matthias

[Anonymous User]

heinrichsweikamp Wrote:
-------------------------------------------------------
> Hello,
>
> We just uploaded the 1.33, it has four different
> salinity settings.
>
> 1.33 Beta
>
> Regards,
> Matthias

Sorry for the late reply/suggestion, but to standardise things I would suggest using the same salinity setting as the X1.

This way people with one X1 and one OSTC can match both instruments to use the same salinity (not that it is a critical feature, but given the OSTC is under continuous development and imrpovement mights as well make as good as it can be).

[sailor]

I don`t think HeinrichsWeikamp is interested in making the OSTC a copy of the X1.

[Anonymous User]

sailor Wrote:
-------------------------------------------------------
> I don`t think HeinrichsWeikamp is interested in
> making the OSTC a copy of the X1.

By using the same Salinity parameters of other computers does not make the OSTC a copy of anything (it is a way to standardise things without an EU Committe and sub-committee meetings).

I wish though the X1 could be cloned at less than half the price just by using the same Salintiy settings!

[heinrichsweikamp]

Hello,

If you look at a salinity map of the Mediterranean sea, for example. Why would a setting of 1.017kg/l (I have no idea which settings the X1 uses) be "better" then 1.020kg/l?

You won't even see the difference of 30cm/100m because the accuracy of the pressure sensor is bigger than that.

regards,
Matthias

[Anonymous User]

I think the topic of the best Salinity setting for your dive computer could make an endless internet forum thread (quite useless though in practical terms).

My suggestion is to align the OSTC with te X1 in terms of salinity settings for the purpose of standardization (not that the X1 got it more right or more wrong than anyone else).

The user can then decide which setting to use and match the X1 and the OSTC to the same salinity setting.

Where I dive it is fresh water 12C on the surface, progressively more brackish down to 6 meters, and thereafter salt water 20C... so I'll pick the salinity setting I think makes sense (particularly from a surveying standpoint) and match it across the OSTC and X1 (currently my two computers one backing up the other... except that the OSTC deco bugs need to be ironed out as a priority).

[divinglog]

From the X1 manual page 24 (www.hhssoftware.com/v-planner-live/V-Planner_Live.pdf) the X1 supports (1000, 1010, 1020, 1025 and 1030 kg/m³). The OSTC supports 1000, 1010, 1020, 1030, 1040 kg/m³. So except from the 1025 the OSTC supports exactly the same settings.

[Anonymous User]

divinglog Wrote:
-------------------------------------------------------
> From the X1 manual page 24
> (www.hhssoftware.com/v-planner-live/V-Planner_Live
> .pdf) the X1 supports (1000, 1010, 1020, 1025 and
> 1030 kg/m³). The OSTC supports 1000, 1010, 1020,
> 1030, 1040 kg/m³. So except from the 1025 the
> OSTC supports exactly the same settings.

Why not just make the two units with the same settings?

If they use the same depth sensor (it would be interesting to know if this is the case), then depths should be aligned (within tolerance).

[sailor]

Hi, salinity adjustment is the most useless thing if ever heard of.
I think HeinrichsWeikamp should focus on the real issues rather then fulfill every useless request on this forum.
I believe the resources are limited and there are much more important issues.
Why dont you ask Liquivision or vplanner to copy the OSTC or it's software.
Thanks for reading, Reiner ( a real fan )

[Anonymous User]

sailor Wrote:
-------------------------------------------------------
> Hi, salinity adjustment is the most useless thing
> if ever heard of.
> I think HeinrichsWeikamp should focus on the real
> issues rather then fulfill every useless request
> on this forum.
> I believe the resources are limited and there are
> much more important issues.
> Why dont you ask Liquivision or vplanner to copy
> the OSTC or it's software.
> Thanks for reading, Reiner ( a real fan )

There is indeed real serious problems which should take priority such as the rewriting of all the deco code.

However, to leave the OSTC set for fresh water only would have been a pity. As the X1 had implemented salinity settings PRIOR to the OSTC, it is only natural for the OSTC to match

[fred]

Hello,

There must be a bug with the Salinity correction. The shown Deep with Salinity at 1.03 was deeper than with 1.00. It is normally the opposite.

=>last dive 90m: the OSTC give me 95.4m

For information, I dive with the V1.33Beta.

Fred.