New Shearwater Dive Modes.

[ReefHound]

That is almost true.

It is in fact based on what it thinks your dive profile is, based on the gas it thinks you are breathing and what GFs you have set.

If you are breathing air and you have EAN32 programmed as the active gas your NDL will be much longer on the computer than it really is.

Decompression is actually based on what gas you are telling it you are breathing and the GF settings.

Maybe that is what you said.

It doesn't think, it goes by what you tell it. The idea that it makes assumptions that you are breathing something else other than what you told it you are breathing is scary. If I thought my DC was calculating my NDL based on an assumption of 36% because that was one of the gasses I have on despite the fact that I am telling it I am on 32%, I'd throw it away before it gets me bent.

 

[ReefHound]

Yes, decompression is calculated based on your actual dive profile BUT your computer’s predicted decompression stops/profile and TTS is based on the assumption that you will switch to a richer gas once you ascend to the richer gas’s MOD for the PPO2 selected for deco. If the rich gas is not utilized for deco or the computer not told of the switch, the actual deco time and TTS will be longer, often significantly, than predicted.

I would never rely much on some prediction based on what it assumes I will do. If this is true, maybe there should be a prediction setting, DYNAMIC to calculate stops and TTS based on assumed switches, STATIC to calculate based on current gas. Or show the two one above the other in different colors.

And isn't what you said also true for overhead environments? The TTS is assuming recreational - that you can begin your ascent now. It has no idea that you are 100' in a cave or wreck and can't ascend for another 5 or 10 minutes.

 

[Pavao]

It doesn't think, it goes by what you tell it. The idea that it makes assumptions that you are breathing something else other than what you told it you are breathing is scary. If I thought my DC was calculating my NDL based on an assumption of 36% because that was one of the gasses I have on despite the fact that I am telling it I am on 32%, I'd throw it away before it gets me bent.

That’s not what he is saying man, read it again

 

[Pavao]

I would never rely much on some prediction based on what it assumes I will do. If this is true…

But it is true and you have always followed some preditction based on assumptions, at the very least on your ascent rate for example.

 

[Capt Jim Wyatt]

It doesn't think, it goes by what you tell it

Excuse my imprecise wording.

I would never rely much on some prediction based on what it assumes I will do

Then you should not dive the Shearwater Tec computers in OC Tec mode because that is exactly what they do. You "tell" it by programming in and turning on your two gases, for example EAN30 for the bottom and 99% O2 for decompression.

During your dive it "predicts" TTS every few seconds based on its' programming that if you leave the bottom NOW and then switch to 99% O2 at 20 ffw your TTS is predicted. This prediction is based on the assumption that the gas switch will occur.

 

[ReefHound]

That’s not what he is saying man, read it again

I'm agreeing with him and pointing out how scary it would be if it did otherwise.

 

[Capt Jim Wyatt]

I'm agreeing with him and pointing out how scary it would be if it did otherwise.

Cool, Roger that.

 

[ReefHound]

Excuse my imprecise wording.

Then you should not dive the Shearwater Tec computers in OC Tec mode because that is exactly what they do. You "tell" it by programming in and turning on your two gases, for example EAN30 for the bottom and 99% O2 for decompression.

During your dive it "predicts" TTS every few seconds based on its' programming that if you leave the bottom NOW and then switch to 99% O2 at 20 ffw your TTS is predicted. This prediction is based on the assumption that the gas switch will occur.

So this Tec mode is making predictions about your technical dive using a basic tenet of recreational diving.

 

[Capt Jim Wyatt]

The image below is from iDEco Pro which also predicts events during a dive. Predicting is planning.

 

[Scared Silly]

That is almost true.

It is in fact based on what it thinks your dive profile is, based on the gas it thinks you are breathing and what GFs you have set.

If you are breathing air and you have EAN32 programmed as the active gas your NDL will be much longer on the computer than it really is.

Decompression is actually based on what gas you are telling it you are breathing and the GF settings.

Maybe that is what you said.

That is what I was implying (modulo the computer's settings). So you are correct to clarify. More complete, decompression is calculated based on your actual dive profile subject to the settings being used by the computer.

Yes, decompression is calculated based on your actual dive profile BUT your computer’s predicted decompression stops/profile and TTS is based on the assumption that you will switch to a richer gas once you ascend to the richer gas’s MOD for the PPO2 selected for deco. If the rich gas is not utilized for deco or the computer not told of the switch, the actual deco time and TTS will be longer, often significantly, than predicted.

But as I noted: That said, in these cases I am planning no-stop dives so I am not concerned.

So all I care about is my remaining gas time. TTS is for intents and purposes meaningless.