Teric Owners - Question(s)

[ClintoKL]

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.

Thanks very much

 

[RobPNW]

To me, it's seems presumptuous for a calculation to be based on the assumption of human action before it's even taken place. If the human doesn't take the action that's assumed most beneficial, than the computer's recommendations would all be wrong.

 

[Joneill]

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).

I just leave 1 gas on (21%) and then use “Edit Gases” to adjust that gas if diving Nitrox. It literally takes a few seconds to do that and it avoids my Teric (or Perdix 2) assuming I’m using a different gas that’s turned on.

 

[stuartv]

To me, it's seems presumptuous for a calculation to be based on the assumption of human action before it's even taken place. If the human doesn't take the action that's assumed most beneficial, than the computer's recommendations would all be wrong.

I can understand your perspective on that.

But, when I am doing a technical dive and carrying deco gases, what it does is exactly what I want it to do.

Once I'm in deco, I don't care what my TTS is calculated to be if it assumes I just keep breathing my back gas and ignore my deco cylinders. What I want - what it USEFUL to me - is having it calculate my TTS assuming I will use the gases I brought in the water with me.

I told the computer I brought these gases. It is implicit that I want the computer to do its calculations with the presumption that I will use them. If I don't want it to do that, then I can simply turn those gases to "Off" in the computer's gas list. If I did that, I would still be able to both physically switch to those gases AND select them on the computer to tell the computer I had switched to them.

 

[RobPNW]

So full disclosure, I have never done a deco dive myself so so I'm just trying to absorb the device logic since I own one.

Given my inexperience, I assume if you have another gas set to on, and it would be beneficial in a deco scenario, does the DC alert you that it recommends switching gas?

If you do switch gas, and set that gas as active after you do, does the DC make any incremental adjustments to the displayed metrics as acknowledgement that you took that action?

What if there's 100% O2 staged, but not physically on you? Would it be best practice to have it listed, but not on and not active, until and when you actually use it?

 

[stuartv]

So full disclosure, I have never done a deco dive myself so so I'm just trying to absorb the device logic since I own one.

Given my inexperience, I assume if you have another gas set to on, and it would be beneficial in a deco scenario, does the DC alert you that it recommends switching gas?

If you do switch gas, and set that gas as active after you do, does the DC make any incremental adjustments to the displayed metrics as acknowledgement that you took that action?

What if there's 100% O2 staged, but not physically on you? Would it be best practice to have it listed, but not on and not active?

The Teric will display your current gas in yellow (I think it's yellow) when you have ascended to the depth where you could/should change to a richer gas. I.e. once you ascend to the MOD of that gas.

For example, if you tell it you are carrying Air, 50% (MOD of 70 feet) and O2 (MOD of 20 feet), then when you ascend up to 70' while breathing Air, at 70' the Teric will still show that you are breathing Air, but it will show the gas in yellow, alerting you that have a gas programmed that would be better to use from 70 on up. When you change to it, the display of the gas will change to show you're breathing 50% and no longer in yellow.

When you ascend further and get to 20', it will go yellow again, alerting you that you could/should change to your O2.

It does not change any metrics shown as acknowledgement that you switched. The metrics are already being displayed on the assumption that you will switch.

If you have a gas staged, and are planning to use it, then you would have it set to On, even though you are not physically carrying it.

If, for some reason, you staged it but are not planning to use it, then you would have it programmed in but set to Off. You *could* (in that case) choose to not even program it in, because you CAN edit gases during the dive, so you could add it in during the dive, in the eventuality that you did decide to use it.

A more likely scenario - though not really recommended - is that you and a buddy are doing a deco dive together but you each have different deco gases. Say, you have 50% and 100%, but your buddy has 32% and 80%. In that case, you'd program your 50 and 100 and have them On, and you might program in 32 and 80 and have them off - for just in case something happens that results in you sharing your buddy's deco gas.

As I said, it is NOT recommended that you are your buddy have different deco gases. But, in reality, it does happen on occasion.

 

[inquis]

If the human doesn't take the action that's assumed most beneficial, than the computer's recommendations would all be wrong.

The likely action is that you will switch, so it's showing you the likely Time To Surface (TTS) and likely time at a given stop. However, that's informational, not guidance. The guidance is "stay above X ft until I say otherwise." Tissue calculations (off-gassing, etc.) use the Active gas and actual depths. It won't clear you to the next depth until those calculations say you can go.

 

[inquis]

@stuartv - Thanks for the experiment and relating the correspondence with Shearwater!

 

[Dan]

I just leave 1 gas on (21%) and then use “Edit Gases” to adjust that gas if diving Nitrox. It literally takes a few seconds to do that and it avoids my Teric (or Perdix 2) assuming I’m using a different gas that’s turned on.

Thanks for sharing your select gas setup. I’ll do the same from now on.

Turn off anything that I don’t need is a good thing in terms of conserving battery too.