Teric Owners - Question(s)

[inquis]

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.

Sorry, still gotta push back when within NDL. Page 30 of the Teric manual states:

All decompression predictions are made assuming you will switch to the best available gas on ascent. At the 21m stop, the breathing gas turns yellow indicating that a better breathing gas is available. If the switch is not made, deco stop and time information will be inaccurate.

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.)

 

[LFMarm]

I am sure I have seen it on my Perdix well before NDL

 

[Dan]

Q1 - Correct.

Q2 - "On" is for gases you actually have with you in the water. "Active" is for the gas you are currently breathing.

So, if you are not carrying a cylinder of 32% in the water with you, it should be set to "Off" in the computer.

When you are preparing for your next dive and you want to make a different gas "Active", you can just select it, without having to turn it "On" first. However, when you do that, you should remember to turn the previous gas "Off" - unless you are also going to carry a cylinder of that previous gas in the water with you.



Don't ever lie to your computer. For example, by telling it you are carrying a gas that you are not really carrying.

If you are breathing Air and you tell your computer that you are breathing Air, but you also have 32% programmed in and set to "On", then your computer will think you are breathing Air, but have 32% available to switch to.

If your computer thinks you are breathing Air and also carrying 32%, then it will calculate your NDL based on that understanding (with the accompanying assumption that you will switch to the 32% at the appropriate time). Generally, for single tank, NDL diving, the difference that makes is very small. Nevertheless, it IS wrong. It is better to simply not do that. Do not lie to your computer. Do not have gases set to "On" unless you are carrying them and going to use them at the appropriate time.

The ONLY reason, in a Shearwater computer, to have a gas set to "On" is so the computer knows to factor that gas into its decompression calculations. It makes the assumption that you will switch to each gas that is "On" when you ascend to the MOD for that gas. 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?

 

[inquis]

Would that be a problem for single tank recreational diving?

Lol, I say no problem and that's a convenient way to quickly switch for NDL diving. Others say your NDL will be initially inflated (unless you're on the richest gas) and will tick down faster (10 min showing on NDL isn't really 10 mins until deco). The jury is out pending empirical confirmation.

 

[LFMarm]

Lol, I say no problem and that's a convenient way to quickly switch for NDL diving. Others say your NDL will be initially inflated (unless you're on the richest gas) and will tick down faster (10 min showing on NDL isn't really 10 mins until deco). The jury is out pending empirical confirmation.

I think that the NDL calculation is based on the active gas so it will be correct. Only caveat is that it will highlight in yellow your active gas is there is another one that is more suitable for the depth you are at amongst those that are on. This is all there is for NDL diving on a single tank.

If you go to deco diving then the problem becomes bigger as it will calculate a wrong TTS and deco plan.

For NDL diving is not a big deal but I hate to dive with an alert that you know has no meaning.

 

[stuartv]

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.

 

[inquis]

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.

This is precisely what @Dan was asking, and I was addressing. I highly doubt it bases it's assumed switching & prompting on having gone below MOD when NDL is nonzero. If I turn on EAN99 and hang out at 40 ft with Air Active, I'm saying it will NOT prompt me to switch as I ascend past 20 ft. The fact there is no prompt (if I'm right) indicates to me it is NOT assuming I will switch on the ascent. Again, all this is when NDL is nonzero.

Yes, turning off all but one gas will work for NDL diving. I still believe having multiple gases On provides identical guidance (to the single gas configuration) while NDL is nonzero AND is quicker to change.

Perhaps that's the test: 2 terics, one with two gases enabled, one of which has a MOD that is exceeded. IF NDL times are identical and no switch prompt is given when passing through the rich MOD on ascent, there is no reason (in my mind) not to use the more efficient approach to setting the single gas for the upcoming recreational dive.

 

[stuartv]

This is precisely what @Dan was asking, and I was addressing. I highly doubt it bases it's assumed switching & prompting on having gone below MOD when NDL is nonzero. If I turn on EAN99 and hang out at 40 ft with Air Active, I'm saying it will NOT prompt me to switch as I ascend past 20 ft. The fact there is no prompt (if I'm right) indicates to me it is NOT assuming I will switch on the ascent. Again, all this is when NDL is nonzero.

Yes, turning off all but one gas will work for NDL diving. I still believe having multiple gases On provides identical guidance (to the single gas configuration) while NDL is nonzero AND is quicker to change.

Perhaps that's the test: 2 terics, one with two gases enabled, one of which has a MOD that is exceeded. IF NDL times are identical and no switch prompt is given when passing through the rich MOD on ascent, there is no reason (in my mind) not to use the more efficient approach to setting the single gas for the upcoming recreational dive.

Fair.

I have 2 Terics and will be diving this weekend. Should be all NDL diving. I will try to remember to perform this experiment.

Also, I emailed Shearwater to ask these questions. I will post when I get a response.

 

[Dan]

AND is quicker to change.

That's my reasoning. After analyzing the % O2 in my next dive tank, I can just scroll down to same % O2 on the list and make it Active (fewer button pressing).

 

[stuartv]

Okay, I will eat some crow here and say I was wrong.

I emailed with Shearwater and they gave me most of the answers to what I asked. Then, I went yesterday and did some diving to confirm what they said and answer the rest of my questions.

So, here's the deal:

Comparing 2 Terics, one set to Air, with no other gases on. The other set to Air (as Active) with 50% and O2 set to On.

The Teric does not give any consideration of gases that are On (but not Active) until you exceed your NDL. That is per Shearwater Support and my own observation yesterday.

Both my Terics showed the exact same NDL, all the way unitl the hit NDL = 0.

Once my NDL got to 0, the Teric set to only Air stayed at 0 for a short amount of time. I didn't time it, but somewhere very roughly around a minute. Maybe a bit less. Then it changed to show a mandatory deco stop at 10' of 1 minute. That is all as expected.

The other Teric (with 50% and O2 set to On) hit NDL of 0 at the same time. But, it then sat there showing NDL of 0 for 2 or 3 minutes after the Air-only Teric was showing a mandatory deco stop.

By the time the multi-gas Teric clicked over to show a mandatory deco stop, the Air-only Teric was showing a mandatory stop of around 3 minutes.

This was all on a dive with a max depth of 64 feet, and my GF Hi set to 70.

So, I said I was wrong. But, I think I can actually make a claim that I was partly, just a bit right. Having extra gases turned on did allow me to stay down longer before my computer showed that I had a mandatory deco stop. And, that would mean that the displayed TTS would be wrong and, if you're using GTR, it would probably be wrong, too.

My experiment only showed a small difference - but I was shallow (relative to a "normal" deco dive). If the extra gases were 30 - 32%, rather than 50% and O2, the difference would be even smaller.

The bottom line: Diving with gases that are anywhere from 21% to 32% Nitrox all set to On won't make any difference at all if you never get to NDL of 0. And after that, the difference in bottom time and displayed TTS will be small.

But, I still assert that you should not dive with any gases set to On other than gases you are actually carrying. I admit that it's a VERY minor issue. But, it still falls under the heading of "lying to your computer". You're telling it you are carrying gases that you are not actually carrying. And so, I would recommend against doing it despite how minor it appears to be.