Modified ratio deco

[LFMarm]

But sometimes people screw up, and it's easy to accidentally select the wrong gas on the computer during an open circuit dive. That's why you need to be able to validate what the computer is telling you. You don't ever want to put yourself in a situation where a single error can cause a serious problem.

An additional way to check if you made mistakes on your computer setup is to compare the TTS with the one from the dive planning software done outside the water. This is a static check that cannot account for on-the-fly changes to the dive plan (like ratio deco would) but can be used to spot significant deviations from what is expected.

 

[lostsheep]

It's trivially true and just basic high school math.

If your computer screws up due to a software defect or hardware failure or user error you need to be able to recognize when it's giving you numbers that don't make sense.

The most likely dive computer failure mode is user error, like accidentally configuring the wrong gasses before the dive or selecting the wrong gas during the dive. If your ratio deco estimate is way off from what the computer is telling you then that's a sign you need to stop and check everything.

If you're so task loaded that you can't do a simple ratio deco calculation (using whatever method you prefer) then you're diving beyond your ability. Time to take a step back.
Technical dive training should be focusing on how to develop thinking divers. Dive computers are excellent tools (I love mine) but you can't have blind trust in them and need to be able to recognize when the output seems wrong, due to either device failure or (more likely) diver error.

Sure, that's part of our equipment check. But sometimes people screw up, and it's easy to accidentally select the wrong gas on the computer during an open circuit dive. That's why you need to be able to validate what the computer is telling you. You don't ever want to put yourself in a situation where a single error can cause a serious problem.

A ratio deco approximation using whichever protocol you like is basic arithmetic which anyone of average intelligence can learn to do with a little practice. Like if you graduated high school then surely you can do this.

I think you're still missing the point or arguing against a strawman but I'll make one final attempt to explain.

In the interest of avoiding strawmen arguments, I too will make one final explanation.

I do not believe I have mischaracterized your stance. You repeatedly suggest a higher likelihood of computer issues while rejecting the possibility of arithmetic errors. I am not anti ratio deco, I object to your characterization that ratio calculations are less likely to induce error compared to the other tools we have at our disposal. You might be right, you might be wrong, but I am unaware of any data that can support a conclusion either way.

ALL of the tools are fallible and ALL should be consistently monitored for erroneous data. To that point , I believe we are in violent agreement.



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[Nick_Radov]

I do not believe I have mischaracterized your stance. You repeatedly suggest a higher likelihood of computer issues while rejecting the possibility of arithmetic errors. I am not anti ratio deco, I object to your characterization that ratio calculations are less likely to induce error compared to the other tools we have at our disposal. You might be right, you might be wrong, but I am unaware of any data that can support a conclusion either way.

I made no statement about the relative likelihood of dive computer failure (including user induced failures) versus ratio deco calculation errors. What I have recommended (and do myself) is to use a dive computer and also cross check the output with a ratio deco calculation: "and", not "or".

 

[rjack321]

If you can't be bothered to add a computer check, including which gasses are configured for the dive, you are diving beyond your ability.

I've heard many a dive shop story of "and then my battery failed" or "I didn't have both deco gasses programmed" and lordy you'd think it was a total disaster.

Vs knowing that a 190ft wreck dive has roughly 5 mins less deco time than a 200ft dive of the same BT, OMG the scuba police are coming to get you.