Apeks DSX TTS logic ?

[Winmit]

Hi,

i was wondering what might be the logic behind the TTS calculation on Apeks DTS. They try to claim it as high tier computer, but I don't see the logic the TTS to be calculated only based on the ACTIVE gas in use. I.e. I set 2 gases - Tx something and pure O2. Planing my dive I want to quit either on low pressure on tanks or on specific TTS lets say 45mins. While diving an with Tx tank active it give me extremely high TTS based only on the Tx, ignoring that I have added a second gas for deco which would be 02. Of course the moment I reach the gas switch and turn to O2, the TTS is recalculated, but to me it doesn't make sense. When I do my dive planning with all the needed gas etc I have 2 parameters to limit my dive - reaching specific pressure(lets say 2/3 in caves) or a specific TTS, again based on the calculation of the gas I will need to go out.

PS. Generally I do see many other strange decisions in the computer. I tried to address them to apeks asking whats the idea behind, but I never got any answer.

 

[ginti]

I am unsure if I follow you.

You would like the computer to tell you the decompression time depending on your plan, right?

What if you don't manage to follow the plan?
What if you decide to change plan underwater?
What if you don't switch gas at the right time, for whatever reason?
What if you lose your deco gas?
What if...?

Telling you the TTS based on the gas you are currently breathing solves all of these issues

 

[Winmit]

i have used a few other computers already and all of them show me the TTS based on the gases I have. including perdix2.
You are correct for "what if....", but how to follow a plan if I don't have a adequate TTS. What will be the maximum time I can stay? I need to relay only on the SPGs as limiting factor.

 

[ginti]

In all honesty, I think the function you would like to have is just slightly more advanced - maybe they didn't think it was necessary... The first version of the Garmin also didn't have this feature, can't speak for the new ones.

Forget what I wrote above, it doesn't make sense

 

[inquis]

Spend some time with a planner to verify that using the backgas-only TTS as an ascent indicator for an open-water dive definitely bounds the deco gas volume on the types of plan deviations you wish do.

In other words, plan a square dive at max depth that is within the constraints of your deco gas volumes. Disable the deco gases to replan and get the backgas-only TTS. Then change the plan to support your intended depth/time variations while keeping the same backgas-only TTS. Re-enable the deco gases and VERIFY that each of the revised deco gas volumes are NOT more than those in the original plan.

Be mindful that there are variations that will increase the required deco gas, in spite of the same back-gas TTS. If you have multiple deco gases, make sure you check each individually for any increase.

 

[inquis]

When I do my dive planning with all the needed gas etc I have 2 parameters to limit my dive - reaching specific pressure(lets say 2/3 in caves) or a specific TTS, again based on the calculation of the gas I will need to go out.

Just saw this portion -- using TTS (all-gas or back-gas doesn't matter) will not work as an indicator for a cave dive, since it assumes an immediate ascent. The increase is also non-linear, so trying to turn a cave dive at a TTS of half of some desired final value will not work either.

 

[Alekseolsen]

Altough Inquis has a good approach to work around the fault computer, I'd just deliver the computer back on warranty, as it's clearly not a tec-capable computer (unless options turns a sensible tts function on).

Even the Suunto D5 calculates tts based on the programmed gases: Quote
When diving with multiple gases, remember that the ascent time is always calculated with the assumption that you use all the gases found in the Gases menu. Always check that you have only the gases for your current planned dive defined before you dive. Remove the gases that are not available for the dive.
Unquote

 

[Winmit]

inquis​

yes, the cave example was not good enough. ut I think you got my point.
I agree with Aleksoelson, wrote to Apeks, but not an answer. Not sure whether it is faulty feature or it was a planned thing.

​

 

[inquis]

Pretty sure it was a design decision, as it's cheaper to implement the simpler algorithm. "TTS" goes on the feature list, and it would be a tiny fraction of buyers who would care about the specifics (single vs multi-gas) AND be able to return it if multi-gas TTS were critical to them.