Breathing rate, air integrated computers and DCI correlation

[RonR]

...
-for those actually doing the calcs, the 20 mm Hg differential takes into account my best guess of the time it takes a DC to re-equilibrate itself during barometric change. Informed input would be most welcome...

The Cobalt uses an absolute pressure sensor (as do many other dive computers) and is constantly tracking atmospheric pressure. It takes seconds to update, and is quite accurate- you could use the pressure display in mBar on the System Info screen as a barometer. You can see how no-stop times change with lowered atmospheric pressure due to altitude or, to a lesser extent, weather. It uses the last pressure reading before a dive starts as the surface ambient pressure for deco calculations. Atmospheric pressure change after a dive starts is something we could not track. But with the barometer falling that fast you might have bigger problems than minor deco differences on getting out of the water.

Ron

 

[Dr. Lecter]

It's actually worse than that. You need to switch the compter between tanks, using a method first seen on digital watches in the (80s?). You have to press a button to cycle between tanks, so not only do you have to make sure you're breathing the right tank, you need to make sure the computer knows which tank you're breathing on.

I have no idea why an AI computer needs a manual tank switch, but it does.



I'm pretty sure it actually calculates that for you, but I've never given it the chance.

As much as I hate defending any aspect of a computer as dated as the Galileo, anything but manual gas changes -- having it alter your breathing gas and O2/deco status based off something other than diver input -- seems like a bad idea. The AI could allow the computer to know when I've changed gases, and then prompt me to confirm, which might be nice.

I'm sure it does calculate AI+deco-based ascent time for you; I know the Cobalt did that, and the Shearwaters will tell you ascent time based on the gas mix it believes you to be carrying, not factoring in whether you have gas to complete that schedule. Still, I assume whatever manual comes with that function advises against using it without or in excess of whatever backup plan it also advises you to have.

 

[flots am]

As much as I hate defending any aspect of a computer as dated as the Galileo, anything but manual gas changes -- having it alter your breathing gas and O2/deco status based off something other than diver input -- seems like a bad idea. The AI could allow the computer to know when I've changed gases, and then prompt me to confirm, which might be nice.

It knows what you're breathing, which is more accurate than what you think you're breathing. In fact, that would let it scream at you if you, for example switched to 80% @ 100', and thought you were on 32%.

A confirmation would be nice "You're now on %50"

 

[Dr. Lecter]

It knows what you're breathing, which is more accurate than what you think you're breathing. In fact, that would let it scream at you if you, for example switched to 80% @ 100', and thought you were on 32%.

A confirmation would be nice "You're now on %50"

On the one hand, I'm not sure I trust its interpretation of pressure data enough to call it "knowing" what I'm breathing. On the other hand, switching to the wrong gas is all too often something humans can't be trusted to do without screwing the pooch. Guess one has to decide which approach they want to trust themselves to.

 

[Tigerman]

On the one hand, I'm not sure I trust its interpretation of pressure data enough to call it "knowing" what I'm breathing. On the other hand, switching to the wrong gas is all too often something humans can't be trusted to do without screwing the pooch. Guess one has to decide which approach they want to trust themselves to.

When talking about mixes with big differences like 32% switching to 80% I would think that the computer messing up by 3% and thinking youre on 29% rather than the actual 32% would be a whole lot better than you messing up and being on 80% when you should be on 32%...

 

[lowviz]

...//... Atmospheric pressure change after a dive starts is something we could not track. But with the barometer falling that fast you might have bigger problems than minor deco differences on getting out of the water.

Ron

Yeah, most of my 20 mm Hg was a very liberal fudge for what I thought took hours to average out in a DC. Thanks for that information, very useful.

And no, I won't be going out in the face of a hurricane that is in the explosive intensification stage...

 

[Dr. Lecter]

When talking about mixes with big differences like 32% switching to 80% I would think that the computer messing up by 3% and thinking youre on 29% rather than the actual 32% would be a whole lot better than you messing up and being on 80% when you should be on 32%...

Wait... what?

I think what we're talking about is whether the computer's interpretation of pressure data is reliable enough to let it decide what of several pre-programmed (including gas blend) tanks is in use by the diver at any given time and basing deco/other calculations on that decision + what the diver has told the computer is in the tank connected to the transmitter in question. I'm not aware of any AI transmitter that also reads O2% and sends that to the computer.

I'm going to stay in the camp of 'adherance to proper gas change procedures should be enough to prevent breathing the wrong mix', but flots makes a good point that at least theoretically an AI computer should be incapable of making such a mistake -- and able to start screaming at you before you tox if you somehow make it.

 

[flots am]

I'm going to stay in the camp of 'adherance to proper gas change procedures should be enough to prevent breathing the wrong mix', but flots makes a good point that at least theoretically an AI computer should be incapable of making such a mistake -- and able to start screaming at you before you tox if you somehow make it.

That was it.

My Galileo really nails the pressure. A single breath drops the reasout by a few PSI, while not breathing a tank leaves it rock steady. I have no doubt that it would be much better than I am about figusing out which tank I'm using, however this also means that thee dive isn't allowed to screw up on the surface by not setting the right PO2 in the computer.

My personal preference is to leave it at home on deco dives, and know what I'm breathing because it's sitting in front of me with a giant piece of tape that says "xx% MOD / xxx'"

It's just too complicated and generally error and failure prone to trust with my life.

 

[HIGHwing]

When the diver goes below 150' the Cobalt switches to a fully iterative RGBM algorithm. This depth is arbitrary, based on not wanting to confuse recreational divers by the schedule shift. The full schedules will start deeper, generally, and look a lot like a very slow ascent. They are based on the Cobalt modeling, in real time, the known physics of bubble formation and trying to minimize that bubble formation through a controlled ascent. On deeper dives, deco is a given, so the limitations above don't apply and we calculate schedules using the full iterative model. While I don't in any sense think of the Cobalt as a Tech computer, this crosses over a bit onto the border lands. So far as I know, the Cobalt is the only recreational computer to incorporate a fully iterative bubble model, though both RGBM and VPM are now available for some tech computers.

Ron

Ron -

Thanks for dropping by and clarifying a few points. I can accept your answer that CPU power vs lawyers that drove the decision of how the model is used. I think it's an interesting point of discussion for this thread, especially considering that some people really believe the computer is the primary brain on the dive. Personally, I like to think my computers are giving my brain some backup information and proceed with the dive accordingly. I made repetitive dives to 165, 198, 235, and 264ft (over as many days) last week and can tell you the percentage of the M-Value I exited on each dive. My main point about the Cobalt was, here's a computer that will suddenly do something different at 150ft, and it's hard for users of technical computers to understand how to mimic the Cobalt's model without endless tweaking on the deeper stuff. To your credit, you're quick to acknowledge the Cobalt really isn't for technical use, so I'm going to agree it's a great computer for the audience it's marketed.

[Not specifc to the Cobalt] It's worthy of note, some of the computers in the market place are essentially masking the computational basis from the diver. I have no way of knowing if the <150ft mode creates more or less stops than the >150ft mode, so we have to play with it to determine what it will do in the planning mode. There is a certain luxury of using Multi-Deco/V-Planner, Baltic or your favorite and looking at a dive and seeing what to expect. I get that computers are supposed to address every aspect of the dive these days, but when you have no clue what they're doing, it's hard to accept. As we saw in the first thread, the dive was fine according to the model accepted by the computer manufacturer, but I personally know that gradient factor used on the dive where the diver was injured does not agree with my body 100% of the time.