OSTC Mk.2 depth difference with other computers/console

[pastaga]

Hello,
Just new happy owner of OSTC Mk.2 and 2 dives with it and Suunto HELO2 commputer as (eventual) back-up. I was diving with APDiving Evolution Vision rebreather.
We noticed (3 divers using OSTC Mk2. computer) 1.6m approximately depth difference at 38m between OSTC Mk.2 (displaying 36m) with Suunto HELO2 and APDiving Vision console (both displaying 38m).
How is it possible ?
How can we adjust OSTC Mk.2 to ensure we have same decompression with other computers/console ?
Thanks for your help.
Best regards,
Frederic.

[ahp]

I have noticed the same differences compared to the Vision. At 90 meters the difference is about 3 meters. The OSTC being deepest. Not sure which one is correct though.
Regards
Anders

[Olivier]

Differences are normal and won't change anything to the decompressions calculs (which are related to the pressure and not to the depth). If you want to adjust your OSTC so that you'll get the same depth on it and on you others computer you can change the salinity factor. But you'll not know if it is the "real" depth...

[Steve]

I know for the suunto if you get into the water and start your descent immediately and you didn't put on your suunto you can have a difference of about 2m. Reason for this is that the suunto calibrates when you put it on. So if you jump in the water and it turns on at 2m this will be equal to 0m. Then you will have a difference of 2m during this dive. This can explain the difference with the OSTC.

Solution for this is to turn on your computer before diving.

[ewatsch]

sorry but do i get this right:
the suunto let's you finish your deco at 5m depth in reality and calculating it as the 3m-deco depth and after that you are allowed to "surface" at two meters depth?

so when ascending to the real surface you should have exceeded the desired maximum tissue tension a little bit...

ah, but i heard the deco-algorithm is really conservative, so there should be no problem!

praise be to our transparent ostc!

[ahp]

True, decompression is related to pressure.
At deeper/longer dives I have seen a difference of the deco-penalty of up to about 20-30 minutes at the moment the dives where aborted (leaving the wreck). Both the Vison and OSTC are using the same gradient factors.
Somehow this must be related to either pressure or difference in the built in algorithm, or?
Regards
Anders

[ahp]

...or ppO2
Regards
Anders

[nemo]

For example Suunto computers are salt water calibrated (see the manual), it means that in fresh water the reading are about 3% smaller. That would explain the 3m difference in 90m if it was fresh water and the calibrations were different.

The salinity setting was discussed in another thread, but maybe the salinity scale in the OSTC could be a bit larger. And it could have pre-settings like "fresh = 1.0kg/l", "salt = 1.03kg/l" and "custom" you could set yourself if needed (for example for the red sea).

ahp Wrote:
-------------------------------------------------------
> I have noticed the same differences compared to
> the Vision. At 90 meters the difference is about 3
> meters. The OSTC being deepest. Not sure which one
> is correct though.
> Regards
> Anders

[honeybadger]

pastaga Wrote:
-------------------------------------------------------
> Hello,
> Just new happy owner of OSTC Mk.2 and 2 dives with
> it and Suunto HELO2 We noticed (3 divers using OSTC Mk2.
> 1.6m approximately depth difference at 38m between
> OSTC Mk.2 (displaying 36m) with Suunto HELO2 and
> APDiving Vision console (both displaying 38m).

Similar observation here, but with the delta the other way.

I dove to 40 meters (according to my OSTC Mk 2 1.70), while my Suunto mosquito and my two buddy's computers all registered ~42 meters.

We had another diver with us, also with a new OSTC Mk2 1.70, who observed the same thing (different buddy pair). The OSTC seemed to read ~5% deeper than the other computers.

Now this is a puzzle. According to Steve, the Suunto might not "turn on" until you are at 2 meters, but if that were the situation then the Suunto would register shallower than the OSTC, and in this case it Suunto read deeper.