PADI tables finally going away?

[Quero]

With tables, you have to plan for the dive, you go down with your limit already set, when you get to the limits, even if your gear is acting up, others will signal to you to either come to the proper depth or stop at the proper time. And if it all fail, tables are more conservative so you have more leeway.

With computer you can simply dive to the limit, and if it acts up, there is no way you can double check its results, you have to thrust in it and you will be walking a lot closer to the edge as they are less conservative and thus you are more prone to accident.

I like safety, so I like a saying from a friend of mine: One equals zero, two is good.

I don't see the computer as a substitute for the rest of the gear, I see it as a very cool redundancy.

Notivago, you must have been told in your open water course that you have to plan every dive, regardless of whether you use tables or a computer to do the planning! Wearing a dive computer to keep track of the data related to the dive does not imply that the diver has no need to plan the dive. You must also have been told that regardless of the means used for planning the dive, the most conservative device used amongst those in the buddy pair/team/group diving together is what everybody follows. If one diver is following tables and the other is following a computer, the one following tables will control the dive; if both are wearing computers, the diver with the more conservative computer controls the dive.

Since you have such a distrust of electronic devices, I hope that the timing device (watch or bottom timer) that you use to track your dive time is a high-quality mechanical one rather than a battery-operated electronic one, and that unlike a great many inexpensive mechanical timing devices, it keeps accurate time.

 

[Paladin]

So, Pete, what would you do if one of your students stated that he did not want to use a computer?

 

[The Chairman]

So, Pete, what would you do if one of your students stated that he did not want to use a computer?

If a student says that they want to learn tables, I would gladly teach him tables. If he is a technophobe, I might suggest that he look into therapy and that diving with a PDC would help him with his rehabilitation.

 

[Paladin]

I'm no technophobe, but the fact is I have more faith in tables. Computers use transistors as logic gates and a dive computer has millions of micro-transistors in it. All it takes is for one transistor to fail and the computer will give false information. The diver would probably not even know that the computer he is relying on is lying to him.

To my way of thinking, relying completely on an electronic device underwater is foolhardy.

I bought a computer last year just to see what all the fuss was about. I've used it a few times, but I kept my watch and depth gauge. To be honest, adding the computer only added another concern about something failing. I don't think of it as something I can trust. I ended up just locking it in gauge mode because depth and bottom time are as far as I would (maybe) trust it.

For me, it was a waste of money. I could have used that cash for something useful.

 

[The Chairman]

I'm no technophobe, but the fact is I have more faith in tables.

Faith is a good way to describe it. There are a number of people who have been "converted" to the infallibility of tables. Their "faith" is based on feelings and not reality. That's OK: it's your dive. Use what works for you.

Computers use transistors as logic gates and a dive computer has millions of micro-transistors in it. All it takes is for one transistor to fail and the computer will give false information. The diver would probably not even know that the computer he is relying on is lying to him.

Transistors and micro transistors are a thing of the past. ICs (integrated circuits) are even smaller and far, far more reliable. As for the computer failing without the intrepid diver knowing, that's nothing but conjecture that flies in the face of the evidence. PDCs either work or they don't. The result is pretty obvious either way. While it's not a phenomenon encountered with PDCs, it's a common mode of failure for mechanical depth gauges and SPGs. I have seen SPGs that showed a pressure decrease only to hang in the middle. I had a buddy show me 1200 on his SPG and be OOA. That was one surprised buddy! I have also seen a few depth gauges off by 20-30 ft at depth and read 0 on the surface.

To my way of thinking, relying completely on an electronic device underwater is foolhardy.

Based on the myths you believe, I can see why. Its a fact: Humans make far more mistakes than any PDC. We are completely unreliable to consistently operate without making a mistake. Add some narcosis and we are even more so unreliable.

To be honest, adding the computer only added another concern about something failing. I don't think of it as something I can trust. I ended up just locking it in gauge mode because depth and bottom time are as far as I would (maybe) trust it.

For me, it was a waste of money. I could have used that cash for something useful.

Protestations to the contrary, it appears that you are a bit of a technophobe. It's not as clear as the anti-robot bias presented by Asimov in "I Robot", but the underlying acrimony is obviously there. That's OK... not everyone needs to dive PDCs. Use what's comfortable for you.

 

[Quero]

.... mine gauge was actually acting up on one of mine last dive, usually I "eat trough" a lot more air than my wife, when she got to 70 Bar mine was still 90 and not changing, I got suspicious and saw little bubbles coming out of the hose in the junction, fumbling with it dropped to 30 bar, not nice.

I'm a little confused by this experience of yours, notivago. Was the pressure gauge that failed an electronic one with a digital display or was it a mechanical one? If it was a mechanical one, don't you think that your story serves to show how mechanical devices can fail rather than how electronic devices can fail?

 

[Blackwood]

Things fail, mechanical widgets, electronic gizmos, and biological wonders (i.e. the human brain) included.

I hedge my bets against failures by diving with at least one redundant diver and, depending on the dive, redundant gauges of my own.

 

[Paladin]

Pete,
Integrated circuits are, indeed, made up of microscopic transistors, diodes and resistors. Advances in electronics technology have not replaced them, they have just become increasingly smaller. I hold an A+ computer technician certificate. I know computers. I know their strengths and their weaknesses. And I know better than to put the absolute faith in them that you seem to have.

A computer operates using logic gates made up of transistors. There are AND, NAND, OR and NOR gates (as well as inverters) in the micro-circuitry of any computer processor. The collective states of these gates determine what the computer is doing at any given time. The failure of a single transistor means a failure, or altered information state, of its respective gate and, therefore, a bit of false information delivered to output or a bit of misread information going to input. The failure of an inverter can do anything from altering I/O data to causing a complete device failure.

My "faith" in the tables is no more displaced or "mythical" in nature than your faith in dive computers. Remember, computers are designed and assembled by us infallible humans, and most likely put together in Asian sweatshops by underpaid, overworked employees.

Pete, since joining SB, I have always respected you and I agree with you on many things, but this is one area in which you and I will never see eye-to-eye.

Dive computers do have their place in helping to make SCUBA a little easier, but over-reliance on technology is just begging for trouble. In my opinion, not teaching the tables (whether or not in conjunction with how to use a computer) is doing a disservice to students. If a diver understands the tables, he will be in a better position to decide if his computer is lying to him. If a computer is to be used, it should be backed up by a watch and depth gauge. I carry two depth gauges: One mechanical and one capillary. A capillary gauge cannot fail. When I use my computer, I still carry the other instruments.

Also, a diver using a computer is more likely to push the NDL and come closer to a situation where a case of the bends becomes increasingly possible. I would be interested in seeing data comparing the number of DCS cases of divers using computers vs. cases where the tables were used. Offhand, I would guess that the majority of DCS cases involve computers.

In 46 years of diving (knock on wood), and using the Navy tables, I have never been bent.

When I look at a set of dive tables, I know what it is telling me. As I look over the numbers, I can visualize what those numbers represent in terms of what happens within my body's systems. The man who taught me how to dive was meticulous and thorough in teaching me not only how to use the (Navy) tables but also the physics (and physiology) of what the figures represent.

I plan every dive, even those in shallow water less than 30 feet, and follow that plan to the letter. I usually dive a square profile because of its simplicity and generally conservative nature but can, and have, planned multilevel dives using the tables.

Do I advocate dive tables exclusively over computers? No. But I most certainly do advocate a thorough working knowledge of the tables, whether a diver decides to use a computer or not.

 

[Blackwood]

I would be interested in seeing data comparing the number of DCS cases of divers using computers vs. cases where the tables were used. Offhand, I would guess that the majority of DCS cases involve computers.

Your guess is probably right, but there's an economy of scale working in there.

It would be interesting. My off the cuff guess is that on average table divers do less in water deco than computer divers.

 

[Kingpatzer]

Also, a diver using a computer is more likely to push the NDL and come closer to a situation where a case of the bends becomes increasingly possible.

Let's assume that it is true that a diver who dives a computer is more likely to finish the dive closer to the NDL of the computer than the diver who dives a table is to finish closer to the NDL of the table. I would note that I see no reason to make this assumption, but let's accept it for argument sake.

Where the proponents of tables seem to go off the rails is assuming that those respected NDLs are equivalent in terms of nitrogen loads of various body tissues (not the theoretical compartments of the model). The underlying mathematical models are simply different between tables and computers. The dive profiles will be significantly different between a diver who dives only square profiles do to planning off of a table and one who dives a multilevel computer dive (indeed if they are both doing a square dive, most computers I've seen actually give less bottom time than the tables, which would reverse your argument!).

In other words, while your conclusion may be correct, if it is correct I don't think you've reached that conclusion using sound logic.

The real metric would not be the number of DCS cases, but the rate of DCS per unit of time in the water at various depth between the two classes of divers.