UTD Ratio deco discussion

[mikeny9]

Sorry I haven't been able to reply to this thread, was busy not internet diving:

So how does Ratio Deco adjust for altitude now?

It's not taught directly as a part of RD, but it is taught that you shouldn't assume RD works for all altitudes. I've never had the chance or the interest to do any altitude diving, but personally I would look at some depth adjustment table or a computer like deco planner or multi deco to figure out what the depth adjustment should be, then just use RD according to the new depth. For example, if I normally dive to 100' at sea level for 30 min on nitrox 32 I would do the same dive only 30' shallower at 70' for 30 min at 10,000 ft above sea level. Why wouldn't that work?

There is a difference between trusting facts like time and depth, and doing math in your head on the fly to come up with an ascent schedule, compared to trusting a device that is computationally precise, and does its computations using the same facts? Yeah. One has all the hard math done by a human. The other has all the hard math done by a computer and the human only has to apply their judgment to modify the results if and as conditions warrant.

But the one that is computationally precise is not computationally accurate. If a digital SPG reads to the nearest 25 PSI but is off by 500 PSI to how much gas I actually have what difference does it make if it's computationally precise?

I am also a software developer by day. If you think that it is a bug when a piece of software calculates an ascent schedule that is too long because it is set for a last stop of 20', all I can say is that I am glad we don't work together.

Yes, it's a common sense bug. Google Maps once plotted a course through a number of countries in Europe that amounted to 2 days of travel or something similar that was about 50 miles between the two points. It wasn't a bug in Google Maps: the border policy prevented Americans from traveling the direct route and an American would have to visit a variety of different countries in order to reach the intended point. Or, the person could use their head and just get a visa and take a 1 hour drive. I'm glad we don't work together either.

Well, at least there was no complex math to do in your head to get to that answer...

What was complex about that exactly? You're a software developer right?

He was quoting my comment about the rebreather program to be dangerous and implying that UTD has had zero RB accidents. Although that may be true UTD has actually only had a handful of RB divers certified and all the ones I know have returned to OC diving. I also know that UTD attempted to modify several rebreathers to suit their program needs only to have the manufacturers of those rebreather remove support for the agency.

I don't use a rebreather and have no interest in one, I don't see the need for one except below 300'. I imagine a lot of UTD people would think the same. Maybe the reason why there are so few UTD people with rebreathers is because within the already small community of UTD people, not many really care to go down that deep.

EDIT: I thought this was a reference to people being bent on Ratio Deco when I wrote this post as well.

Yes, UTD will tell you that there have been zero incidents using Ratio Deco. They were saying the same thing when i was arguing with Andrew about it.

I am trying to remember exactly, but when we talked our small Rocky Mountain UTD group had had six DCS cases, with two resolved by surface oxygen, two resolved by in-water recompression, one resolved after a number of days of chamber treatments after driving home to Colorado, and one resolved after a series of chamber treatments following a helicopter evacuation.

So in your opinion, the reason was the use of RD? What other evidence do you have that suggests it was purely RD? Were they depth adjusting like I mentioned above or did they just assume RD works for all altitudes like you did? It's easy to point the finger at RD, but from what I've seen it tracks 20/80 fairly close. There must be a lot of people getting bent on 20/80 then too. There are also a lot of people using RD and 20/80 with no problems but we never hear about those.

I decided to leave UTD (about 6 years ago) just prior to heading to Florida for a month...

Weren't you booted from UTD for teaching students without having them complete their liability paperwork?

Personally, I would love to read more from recent graduates. We have a bunch of old men bickering about this and that. It's been interesting, but I really want to hear from 20 and 30 somethings about what they were looking for when they took a UTD class and how it worked it out for them.

I'm 36, in the past two years I've taken a number of UTD classes and GUE/F. What would you like to know?

The above is what it used to look like before Ratio Deco 2.0 came about. I would assume the first stop would be at 66 feet instead of 75 for a dive to 100?

You'd round shallower, so 60'.

 

[stuartv]

But the one that is computationally precise is not computationally accurate. If a digital SPG reads to the nearest 25 PSI but is off by 500 PSI to how much gas I actually have what difference does it make if it's computationally precise?

Dive computers, by and large, are also very computationally accurate. They tell you pretty much exactly what the model says.

Are you suggesting that a human, doing multiple steps of math, is going to be more accurate - or even AS accurate - as a computer, when they are both performing calculations using the exact same input data? Let's keep in mind that the human using the computer can still apply modifications to the calculated result based on how they feel, whether it's cold or dark, etc...

It wasn't a bug in Google Maps

So good we can agree on that.

The scenario you described earlier doesn't sound like it was a bug, either. Unless you're saying it gave incorrect results for the input data it was given (including however it was told to determine the last stop depth). If it was told to use a last stop depth of 10' and it calculated for 20', then sure, it was a bug.

 

[mikeny9]

Dive computers, by and large, are also very computationally accurate.

Computationally accurate to their model, but the model may not be accurate, it's a model after all. So yes, I think my brain and my backup brain (my buddy) has more common sense than a computer.

The scenario you described earlier doesn't sound like it was a bug, either. Unless you're saying it gave incorrect results for the input data it was given (including however it was told to determine the last stop depth). If it was told to use a last stop depth of 10' and it calculated for 20', then sure, it was a bug.

It illustrates my point perfectly. Yes, there is no bug in the software, just a bug in common sense. Brains have common sense, computers don't.

 

[stuartv]

Computationally accurate to their model, but the model may not be accurate, it's a model after all. So yes, I think my brain and my backup brain (my buddy) has more common sense than a computer.

And so...?

Are you suggesting that a human, doing multiple steps of math, is going to be more accurate - or even AS accurate - as a computer, when they are both performing calculations using the exact same input data? Let's keep in mind that the human using the computer can still apply modifications to the calculated result based on how they feel, whether it's cold or dark, etc...

We have seen cases (more than 1, if I'm not mistaken) described right here on SB where experienced divers, experienced with RD, have gotten bent because they BOTH messed up their mental calculations.

Are you aware of any cases of 2 divers with 2 computers each where all the computers got the calculations wrong?

 

[mikeny9]

And so...?

What are you asking?

We have seen cases (more than 1, if I'm not mistaken) described right here on SB where experienced divers, experienced with RD, have gotten bent because they BOTH messed up their mental calculations.

Are you aware of any cases of 2 divers with 2 computers each where all the computers got the calculations wrong?

Can you post a link?

Have I heard of cases where 2 divers using 2 computers got the computer's model calculations wrong? Nope. I have I heard of cases where 2 divers using 2 computers got bent because the model wasn't good enough for the conditions they were in? Yep.

 

[boulderjohn]

It's not taught directly as a part of RD, but it is taught that you shouldn't assume RD works for all altitudes. I've never had the chance or the interest to do any altitude diving, but personally I would look at some depth adjustment table or a computer like deco planner or multi deco to figure out what the depth adjustment should be, then just use RD according to the new depth. For example, if I normally dive to 100' at sea level for 30 min on nitrox 32 I would do the same dive only 30' shallower at 70' for 30 min at 10,000 ft above sea level. Why wouldn't that work?

Because it isn't that simple. It is not a basic linear relationship. You are also using an example from mindeco, which is not really Ratio Deco. We were doing decompression dives, not shallow recreational dives.

So in your opinion, the reason was the use of RD? What other evidence do you have that suggests it was purely RD? Were they depth adjusting like I mentioned above or did they just assume RD works for all altitudes like you did? It's easy to point the finger at RD, but from what I've seen it tracks 20/80 fairly close. There must be a lot of people getting bent on 20/80 then too. There are also a lot of people using RD and 20/80 with no problems but we never hear about those.

there is a book's worth of material to respond with here. I will try to pick out a few points.

First, they were doing exactly what they were taught: using RD exactly as it was defined without making any adjustment for altitude. I can say that emphatically because it was a reason for raging debate for me. Andrew told me he knew that there was no need to adjust RD for altitude because he dives at Lake Tahoe without adjusting for altitude, and he does fine. (This would be, of course, in between his competing in ironman triathlons.) If he's fine, everyone would be fine.

When scientists do testing and statistics for different algorithms, they do not exclude negative results for people who MIGHT have an underlying cause. For example, one of the reasons offered by UTD for a person's DCS was that the person MIGHT have a PFO--that person has still never been tested for a PFO, so it was just a guess. In testing, people with PFOs are included in the results, and they especially do not exclude people who MIGHT have PFOs. When evaluating an algorithm scientists do not assume that the algorithm is perfect and exclude all cases of DCS for that reason.

Weren't you booted from UTD for teaching students without having them complete their liability paperwork?

Well, you have apparently been fed a lot of misinformation already, but this one is a whopper. I was never a UTD instructor, so that could not have happened. Additionally, when I was with UTD, all that "paperwork" was handled online through their headquarters.

I left UTD when they threatened to report me to PADI for posting a thread on ScubaBoard that asked questions about using ratio Deco at altitude. They said that this was a derogatory statement against them, and since PADI standards do not allow its professional members to make derogatory comments about other agencies, I would face discipline and possibly lose my PADI instructor certification.

 

[mikeny9]

Fair enough John. I can say at least now, they don't teach that RD is the same for all altitudes.

 

[boulderjohn]

We have seen cases (more than 1, if I'm not mistaken) described right here on SB where experienced divers, experienced with RD, have gotten bent because they BOTH messed up their mental calculations.

Can you post a link?

I have described this event several times. I will be happy to do it again.

In the case in which two of my friends who got bent using RD, one of them was using a computer in gauge mode, so they had a computer log of the dive they did and could compare it to the dive they thought they did. It turns out they made three separate and fairly significant miscalculations during the dive--we are talking basic arithmetic here. One of them had aPh.D in computer science, so we are not talking about people who are math-challenged. These three miscalculations led to them being wrong on their average depth, their ascent rate to their first deep stop, and the amount of time they spent on their last deco stop.

 

[boulderjohn]

I just made an additional comment about that last story that is germane to this thread.

UTD Decompression profile study results published

 

[mikeny9]

Interesting, so all of those things your friends miscalculated I use a computer for: average depth, ascent rate, and I run a stop watch on it when I start my ascent. In my opinion, computers/digital bottom timers are much better at this than the brain. However, I always have a pretty good idea what my average depth is and what my ascent rate is, and I use the computer to verify it. I don't let it run my ascent though, that's my responsibility.