Shearwater Teric - a few questions on how it works!

[Rearviewmirror]

Hi all,

I've had my Teric for ~10 dives now and absolutely love it. BUT I got certified originally in the stone age (manual tables were the order of the day) and computers were a comparative rarity. I have found the Teric manual to be a bit sparse on the "how" things are happening in more basic language - presumably as it's aimed at more experienced/tech divers who may already know all of this. I wanted to ask a few questions to make sure my understanding is correct:

1. Am I right in thinking that as long as I wear my watch on all my dives, all the metrics I'm shown (NDL, tissue loading, ppO2) take into account everything I've done in terms of diving? (I am 99.9% sure this is right, but worth confirming!)
2. Whenever I am planning a dive in terms of depth/NDL and switch my selected gas to Nitrox 32, presumably that is also factoring in all my previous dives? The manual says "The Deco Planner does not provide thorough validation of the profile. For example, it does not check for nitrogen narcosis limitations, gas usage limitations, CNS percentage violations, or isobaric counter-diffusion risks due to sudden helium switches" but I assume it does factor in other aspects of prior dives?
3. Am I right in thinking there is no way to enter tank size to have the Teric/Shearwater Cloud to calculate RMV?
4. Is there any field on my dives where I can track RMV in Shearwater Cloud after manually working it out and then graph it?

Thanks!

 

[Marie13]

First question: are you using it in the receational mode?

First question: yes.

I can answer to third question - no. To get RMV info, I had to download dives from my Perdix into MacDive (which I’ve been using for a while), indicate tank size, and then got RMV.

Last question: I believe there is a notes field you could use for that info.

There are some YT videos on Shearwater computers that may help.

 

[Wibble]

The RMV / SAC needs an Air Integration (AI) transmitter to provide the pressure data and thus the usage.

There's no affect if you're doing the next dive with 32% compared with the previous 21% (air). Obviously you'll get the benefits of the Nitrox, but the calculations will start from the point at where you jump in.

Their warning is just CYA blather. They're saying

• That you need to ensure you don't exceed the MOD (max operating depth) on your, for example, 32% nitrox.
• That you don't run out of gas (you use a lot more when you're deep or stressed)
• That narcosis is a fact (generally below about 30m/100ft it affects most people, some a lot more than others.
• CNS is really only applicable if you've done a longish dive with oxygen gasses.
• IBCD is all about helium mixes (deep, lots of gas switches, very technical, affects very few people).

Shearwater kit is great. Trusted by lots of technical divers (including me!), so a lot of their kit goes to deep and long duration dives way beyond "recreational diving" limits which is basically diving within the No Decompression Limits (NDL). The best thing about their kit is it works really well for recreational diving too.

 

[Rearviewmirror]

Thanks Marie I tried to find all the YouTube videos I could but couldn't find that info. I'll try another search!

Yes - I am using it in OC Rec mode.

Wibble - I am using it AI, and so I'm getting SAC rate, but have to manually calculate RMV (no way to select tank size with the Teric as far as I can see)

 

[Ukmc]

Yea it will keep track of your prior dives, NDL for repeated dives and O2 CNS percentage.
I do not use shearwater cloud for dive logging. Other apps/programs will calculate RMV for you automatically.
For example, I use Divelog app that will do it for you. As a bonus, it will grab a GPS location of your dive site and will plot them on the map. Kind of cool.
Enjoy your Teric. It is a fine dive computer!

 

[loosenit2]

Am I right in thinking that as long as I wear my watch on all my dives, all the metrics I'm shown (NDL, tissue loading, ppO2) take into account everything I've done in terms of diving? (I am 99.9% sure this is right, but worth confirming!)

Correct, kind of. It will take anything into account that matters to tissue loading. It will not take into account dives that are irrelevant to your tissue load (i.e. a dive after a Surface Interval of two weeks).

Whenever I am planning a dive in terms of depth/NDL and switch my selected gas to Nitrox 32, presumably that is also factoring in all my previous dives? The manual says "The Deco Planner does not provide thorough validation of the profile. For example, it does not check for nitrogen narcosis limitations, gas usage limitations, CNS percentage violations, or isobaric counter-diffusion risks due to sudden helium switches" but I assume it does factor in other aspects of prior dives?

CORRECT. The Teric will tell you if you are about to do something that will erase tissue loading data. For example if you update the firmware it will tell you that you are going to erase tissue loading history and you can chose to do it or not.

1. Am I right in thinking there is no way to enter tank size to have the Teric/Shearwater Cloud to calculate RMV?

CORRECT

1. Is there any field on my dives where I can track RMV in Shearwater Cloud after manually working it out and then graph it?

NO...Way to do RMV at all. Cloud will let you enter tank size but it is treated alphanumeric data field, will not calculate RMV on Teric or in Cloud.

 

[Wibble]

RMV v. SAC confuses the hell out of me. Never have worked out what the difference is. All I know is that I need to know my SAC (surface air consumption) in litres per minute and then just multiply it by the atmospheres I'm diving at (conveniently it's 1 atmosphere per 10 metres depth).

So a SAC of 20 litres/minute (moderately high) will mean that at 30m/100ft, where the pressure is 4 atmospheres, I'll be consuming 20 x 4 = 80 litres of gas every minute and will empty an ali80 (which contains about 2000 litres of gas) in 2000 / 80 = 25 minutes

 

[Rearviewmirror]

Correct, kind of. It will take anything into account that matters to tissue loading. It will not take into account dives that are irrelevant to your tissue load (i.e. a dive after a Surface Interval of two weeks).


CORRECT. The Teric will tell you if you are about to do something that will erase tissue loading data. For example if you update the firmware it will tell you that you are going to erase tissue loading history and you can chose to do it or not.

CORRECT


NO...Way to do RMV at all. Cloud will let you enter tank size but it is treated alphanumeric data field, will not calculate RMV on Teric or in Cloud.

Awesome - thank you!

RMV v. SAC confuses the hell out of me. Never have worked out what the difference is. All I know is that I need to know my SAC (surface air consumption) in litres per minute and then just multiply it by the atmospheres I'm diving at (conveniently it's 1 atmosphere per 10 metres depth).

So a SAC of 20 litres/minute (moderately high) will mean that at 30m/100ft, where the pressure is 4 atmospheres, I'll be consuming 20 x 4 = 80 litres of gas every minute and will empty an ali80 (which contains about 2000 litres of gas) in 2000 / 80 = 25 minutes

My understanding is that you can only compare SAC rates across dives in a meaningful way if you are always using the same tank size (not an issue for me so far as a humble rec diver) but RMV is a truer representation as it corrects for tank size (so if you wanted to compare your numbers to another diver/yourself over multiple tank setups you can do so more easily).

So to anchor that in an example, if I have an 80cuft tank at 3000psi and a 100cuft tank also at 3000psi - my SAC rate will show a lot lower (I think that's the right direction) for the larger tank, because consuming 10cuft of gas from the larger tank will reduce the tank pressure in PSI proportionally less than breathing up 10cuft from an 80cuft tank. So while SAC is adjusted for depth - you also need to know volume consumed to track gas consumption in a normalized way. Sadly tank transmitters only see pressure change, not volume consumed.

 

[Manatee Diver]

My understanding is that you can only compare SAC rates across dives in a meaningful way if you are always using the same tank size (not an issue for me so far as a humble rec diver) but RMV is a truer representation as it corrects for tank size (so if you wanted to compare your numbers to another diver/yourself over multiple tank setups you can do so more easily).

SAC vs RMV is a tricky. Until recently SAC could mean pressure/min/atm or it could mean volume/min/atm, you had to include the units so people know what you were talking about. So someone figured why don't we use RMV for volume to lessen the confusion. I personally hate RMV, it is a medical term that has a close meaning, but it is different enough that it can cause confusion and problems. If we are going to use two different terms we should make our own term instead of coopting a medical term. Or we should be like my science professors in college and require units to get full credit. /rant

But in order to do a proper comparison the raw SAC pressure data out of Shearwater cloud needs to be turned into volume. Third party programs can do this. @Marie13 mentioned Macdive but as you can guess by the name it is Mac/iOS only. Subsurface works across all platforms, and is very popular.

 

[inquis]

Is there any field on my dives where I can track RMV in Shearwater Cloud after manually working it out and then graph it?

I use Subsurface, which provides this graphing capability. (They refer to it as SAC, but it has units of vol/min, which is what you want, aka RMV. I'm in the "just use units" camp, as they're both consumption rates normalized to the surface.)