Another Tables vs. Computers Thread

[Rick Murchison]

Here's my post from the other thread... it is germane here:

What is needed is a feel for "what's reasonable?" You can know how to use the tables cold, but unless you incorporate what the tables are telling you into your personal TLAR diving envelope you can still make an egregious error. Computers, being computers, can make *really* egregious errors from time to time, and unless you have a feel for what's reasonable you can go merrily on your way and do something really stupid based on what the computer tells you, or, even worse, miss a dive 'cause the computer says you can't go when in fact you can.
If you're one who really believes a computer "always" makes the same calculation the same way every time and you don't believe computers screw up in a big way from time to time then you're living in a fantasy world. It is not a matter of whether the computer will give you bad information sometime, just a matter of when... and whether you have enough of a grounding in what information is reasonable to recognize it.
My personal solution is to (1) run my own approximation of what the computer ought to be telling me before I ever look at it, and (2) carry either a backup computer or at the least a bottom timer and depth gauge in addition to the computer. I have yet to use or to see a computer brand that hasn't given bogus info from time to time.
Rick

Rick
__________________

 

[BHB ScubaTroll]

The difference between flying and rec diving on nitrox is that when rec diving you can terminate a dive at any time as soon as your computer fails. If your avionics fail in a plane, you still need to find an airport and land (you need to know where you are, where the winds will push you, etc.) If a computer battery fails, you end the dive and don't get to dive for 24 hours unless you have kept track of your N2 & O2 apart from the computer. This is the only risk I see with solely using a computer. You ARE dependant on your computer, but for most divers with no deco obligation, it doesn't matter. Computer failure = ascend to 15 feet, safety stop, surface, don't dive for 24 hrs and get computer fixed. The theory behind nitrox is still taught, you just have a different means of obtaining the information.

Airport would be nice, but usually not available in most power failure issues....

And,I CHOOSE a simple method that affords me the opportunity to continue my current dive as planned, AND, continue diving for the next 24 hours/beyond while the computer is being fixed...

Easy is as easy does (That's what momma always said....lol)

 

[minnesota01r6]

I think people posting in this thread are forgetting the fact that you can make your own tables by using the dive planner built into a nitrox computer. plug in different depths for a given mix at 1.4 pp02, and you have the NDL time limits of that gas at that depth. Enough experience with this will give you the ability to predict what your computer will tell you just like studying the tables will, and you will KNOW if something is wrong and you plugged in EAN40 instead of EAN32 or you set pp02 to 1.6.

EDIT: cooltech - I agree, the tables are good, and every competent instructor tells you to backup even your air dives with table calculations, keep track of your pressure groups, etc. What I am saying is that there are many divers who would rather not be bothered by tables, accept the fact that they may forefit the ability to dive if their computer fails in return for not having to calculate by hand, and they don't loose any margin of safety. A mistake can be made in table planning as well as computer planning, and the best way to counteract this is to plan with a buddy, both do calculations separately for planned depth, mix, & time, and then compare the results.

 

[tedtim]

Quoted from another thread:

Ignoring issues of reliability, just considering understanding of decompression, why do so many people repeatedly say that learning to use the deco tables in OW is preferable to learning to use a computer?

Because the battery in a table never goes dead.

the K

I suggest that there are two lines of thought here. One is regarding planning and the other is regarding following the plan/adjusting to circumstances.

Total dependency on a computer can lead to a situation such as the K describes. If you are diving solo then you would be in a real world of hurt. Even the tables that I have used describe a procedure if you exceed the NDL. One of the silliest questions that I saw on a closed book test was to describe the procedure if you exceeded a NDL by more than five minutes. You needed the tables to do the dive profile questions and the procedure for the action to be taken if a NDL was exceeded is printed on the table. The intent was that the procedure should be memorized. In situations where stress is increased the memory can be faulty. I doubt that many recreational divers regularly review this type of information. So, if your computer dies underwater, pull out the table that you carry with you and follow the procedure.

Sorry, but I really don't believe that everyone has to memorize non-critical procedures, formulas, or tables when there is an aid available to you. Checklists were created for a reason. Yes there are critical emergency situations and you should practice the skills for those situations. If your computer dies on a recreational dive it is not critical that you take immediate action. Stop, breathe, think, act. An immediate response in this situation is a recipe for disaster.

What is wrong with getting together with your buddy, doing a safe ascent with the appropriate safety stops as if you had exceeded the limits, and sorting it out once you are out of the water? My first line of thought here is that I need to determine what I should do to get away from making the problem greater than it is.

The tables are for planning. Not following the plan is a problem. You can use either the tables or your computer to plan. If your computer battery dies while you are using it for planning, then you can't use it underwater anyway. Underwater, carry a watch or other bottom timer as a backup. Dive with a buddy. Work with the buddy to resolve the problem safely.

 

[rottielover]

Well instead of responding in that other thread I thought I would respond here:

"Why does anyone think that knowing how to read a table provides an understanding of "what's going on"?"

Well actually other's pointed this out for me already, you get an understanding of "what's going on" from your basic OW class. Once you've learned the theory, you then learn how to apply that theory using the tables and computers. I believe you gain additional insight into what's going on inside that fancy calculator (yes ALL computers are fancy calculators) by learning how to use the tables, and in the case of the nitrox class, the math. After all, the tables are just a nice "chart" of calculations already done for you. You could either take your depth and time and do all the math, or you can run the table where that calculation has already been done and written down for you to use.

"How do the numbers on the tables better represent the formulae and algorithms used to calculate decompression than the display of a dive computer or the output of a deco program?"

I don't think the tables "better represent", I just think the tables are the "baseline" or "standard" that can/should be used to better judge if the computer/program is giving you accurate information.

Would learning the Wheel give you an even better understanding of "what's going on"?
How does learning table reading make you understand physics or physiology?
What math did you study to understand "what that fancy calculator on your wrist/console is really doing"?

I am not familiar with the wheel, so I don't feel that I can or should comment on the wheel other than to say that I have seen and heard other's call it "dial - a - bends".

The tables do not give you an understanding of physics or physiology, your basic OW class gives you the information you need in those area's already. As for the math, it's pretty basic level algebra, you know X = (D-33)x(.36-10) [NOT AN ACTUAL FORMULA!!]

I just think you might have missed the point of my post in the other thread, which was to provide my perspective as a nitrox student, fairly new diver on the topic, and to articulate that view point to other students and instructor's in the hope that it will aid them in some way.

Computer's are great, but I work on them every day in my job as a Systems Administrator (MCSE). I know the how/why of computer failures, and I also know from experience that they always seem to fail "at the wrong time".

So as one poster pointed out, you could relay solely on your computer, and if it fails, end your dive and stay out of the water for 24 hours (longer if it takes longer to get it repaired/replaced). OR... you can run your numbers with tables, switch to a watch/depth gage and continue your expensive dive vacation.

Another MAJOR problem I see all the time is the "garbage in - garbage out" problem... While it's true that running the tables with wrong numbers will give bad results, the same is true for setting your mix wrong in the computer. Something that I'm sure SOMEONE out there has done at one point or another. My understanding is that most dive computers will "reset" to 21% after a dive, so what if for some reason you forgot to change that over to say, 36% ?

Automation is great, but you have to have a process in place before you can automate it. I see this all the time at work, "we want to the computer to do this, and this and this, and we want to push one big read button and EVERYTHING will work, right?" Well, if you don't have some sort of business process, behind what the computers are doing, your in for some major trouble.

Well I hope that helps out!

 

[ReefHound]

The original poster clearly said "ignoring issues of reliability" yet so far all the responses are about equipment failure...well, at least you got the ignoring part!

That's like saying "other than the risk you could fall and die, what's the point of wearing a safety harness when working in high places?".

You can't just exclude an integral part of the equation and expect the result to have relevance. I think people are showing the wisdom to ignore such a silly exclusion because reliability is at the heart of the issue.

Other than that, Mrs. Lincoln, how was the play?

 

[minnesota01r6]

computer reliability DOES NOT EQUAL safety. If your computer or bottom timer fails, you thumb the dive and make a conservative safety stop. A competent diver in either situation would recognize the failure before exceeding NDL limits. An incompetent diver in either situation is in trouble.

 

[MikeFerrara]

I think people posting in this thread are forgetting the fact that you can make your own tables by using the dive planner built into a nitrox computer. plug in different depths for a given mix at 1.4 pp02, and you have the NDL time limits of that gas at that depth. Enough experience with this will give you the ability to predict what your computer will tell you just like studying the tables will, and you will KNOW if something is wrong and you plugged in EAN40 instead of EAN32 or you set pp02 to 1.6.

I don't think any one is forgetting that althoug not all dive computers make that very convenient. You could also use other software to run all kinds of tables. IMO, hvaing the information in advance is what allows you to use it in a proactive way. I don't know that it matters where you get it.

EDIT: cooltech - I agree, the tables are good, and every competent instructor tells you to backup even your air dives with table calculations, keep track of your pressure groups, etc. What I am saying is that there are many divers who would rather not be bothered by tables, accept the fact that they may forefit the ability to dive if their computer fails in return for not having to calculate by hand, and they don't loose any margin of safety. A mistake can be made in table planning as well as computer planning, and the best way to counteract this is to plan with a buddy, both do calculations separately for planned depth, mix, & time, and then compare the results.

Lots of computer dives will run you off the tables because of the single level nature of most tables. that can make using tables as a backup pretty hard. What will work, and there are many ways to do it is to have multileve schedule ahead of time that covers your dive. Then you can easily switch from the computer and continue diving.

 

[H2Andy]

how could it hurt to know more than one way to accomplish something?

how could it hurt to know only one way of accomplishing something?

that's why i know how to use tables and computers

 

[Daner]

Isn't a computer just a fancy case for the tables? It's what you do with the information they provide that is really important. Most divers I have seen, that don't use computers, aren't reading their tables under water as far as I can see. They use them before and after.

For a properly planned dive, a computer failure should mean nothing more than continuing your dive as planned or aborting the dive. After the dive I can choose to relax for 24 hours and not dive or work out my previous dives in the current series of dives using the tables and continue on.

Qualifications: In addition to my computer I still have an SPG and depth gauge. I don't have a backup timer because I have a buddy for that whom enters and exits the water at the same time I do (and if his computer or time fails then we would surface and head to the nearest lottery vendor). I always (at least to date) dive within recreational limits.