I agree it assumes you will switch once you're in deco, but I'm nearly certain it bases remaining NDL time on the Active gas rather than "best Available". (The fact you are NOT prompted to switch to a deco mix on the initial descent of any tech dive somewhat corroborates that.)
I'll check the next time I'm out, but I contend that the displayed NDL at depth will increase upon switching the Active gas to any richer EAN.
Your experiment to confirm your theory is flawed.
The Teric is assuming you'll switch when you are ascending. It is not assuming you'll breathe the richer gas during the bottom phase. So, switching to a richer gas while you're just hanging out on the bottom definitely SHOULD increase your NDL.
It matters also for NDL dives. Thanks f you switch on multiple gases, the computer will keep advising you to switch to the best (highest O2% within the allowed pO2 limit) by highlighting in yellow the current gas. It doesn’t affect your dive calculation unless you actually switch to that gas however it’s not best practice to dive with an alert on that can distract you
Yes, it does affect your dive calculation. The decompression (whether there is a mandatory stop or not) is calculated assuming you're going to use the gases you told it you are carrying.
Sorry, still gotta push back when within NDL. Page 30 of the Teric manual states:
Again, the assumed switch as well as prompt to switch is in the context of a decompression dive.
It'll be a few days before I can get wet. If anyone else gets out sooner, please let us know after explicitly looking for this behavior (a prompt to switch gases while NDL > 0). Additionally, IF remaining NDL is tied to "best available" gas, it would necessarily tick down faster than realtime when that gas is not Active. (Make sure you stay above the richer gases MOD.)
All dives are decompression dives. Some have mandatory stops and some (NDL dives) don't.
The part of the manual that you quoted spells it out quite clearly. "ALL DECOMPRESSION PREDICTIONS" is a phrase that encompasses when you enter into mandatory decompression stops, as well as what the stops are and for how long.
"Deco stop and time information" will be inaccurate. That includes the difference between a deco stop at 10' and a deco stop at 0' (i.e. no mandatory stop).
The Teric factors in the time it takes to ascend. If you are breathing Air and have no other gases On, then it will assume an ascent from (for example) 100 feet is going to take 3 1/3 minutes. When it determines that in less than 3 1/3 minutes of breathing Air, you will have enough nitrogen load to need a mandatory deco stop, then your NDL will show as 0.
On the other hand, if it thinks you are going to switch to EAN36 at 96 feet and then breathe that on the way up, it will calculate that you will absorb less nitrogen during the ascent. That means you can absorb more nitrogen on the bottom before you get to the point where your ascent would require a mandatory deco stop. Thus, it would give you a longer NDL.
Also, as I said earlier, the difference between these things is going to be very small. My expectation is that the difference is so small that rounding things to the nearest one minute will erase any "seen" differences.
The only thing I'm not really clear on myself is how it handles it if you have a gas that is On (but not Active) that you could be breathing for the whole dive. Example: You do a dive to 100 feet. The MOD of EAN32 is 111 feet. You do the dive on Air, but you have EAN32 programmed in and set to On.
As you (I think?) already noted, the Teric does not prompt you to switch to EAN32 during your initial descent. So, when, if ever, would it prompt you to switch? And if it never prompts you to switch, then is it using that gas in its deco calculations or not? If so, what depth does it calculate that you will start to use the EAN32? Maybe it calculates its predictions continuously on the assumption that you are going to switch to EAN32 immediately.
My theory is that it only prompts you to switch if you have gone below the MOD for that gas. Then, when you come back up to the MOD for that gas, it prompts you to switch. And, of course, in that case, I'm confident that it assumes you will use that gas.
All that said, if you follow the simple rule I posted earlier, it will never be an issue. I.e. For single tank diving, one gas should be Active and all others should be Off.
I pre-set “Select Gas” to 32%, 31%, 30%, 29%, 21%, and turn all to on with Active on 32% for my current dive (as shown, below). If my next dive is on air, I just scroll down 21% and make it active. Would that be a problem for single tank recreational diving?
I believe my post, which you quoted, answered this question quite clearly.
For single tank diving, one gas should be Active and all others should be Off.