Another Tables vs. Computers Thread

[Blackwood]

I think this is a great question and one that I've thought about a lot. All I can really say is that taking the time to compare different models and taking care in how I apply them in progressing to longer and deeper dives has seemed to work for me.

Sure. Again, I agree... based on my experience. But I think we're discussing new divers who, by definition, can't have such experience.

I dive Buhlmann ZLH-16 tables and I like them. I, too, have never had a chamber ride. But there are different tables and, moreover (bringing in enriched air), discrepancies between tables of the same variety. For example, you can read the IANTD (ZLH-16) table for Nitrox to find your bottom time. You can solve for EAD and use the IANTD (ZLH-16) table for Air and get a substantially different bottom time*. Why? Rounding. The tables show depths in 10 foot increments. With a computer, you get depths in 1 foot increments**. So which is better, especially for a new diver?






*Example: 56 FSW, Nitrox II -> EAD = 39 FSW.

The IANTD Open Water Air Diving & Decompression Tables say the NDL for 39 (rounded to 40) FSW is 125 minutes.

The IANTD EAN 36% Diving & Decompression Tables say the NDL for 56 (rounded to 60) FSW is 75 minutes.

Using a computer, that rounding error will be of a much tighter magnitude.

How can we expect them to make a good judgment call?


**I know in planning mode you are stuck with 10' incriments a'la the tables. I'm assuming that you are credited NDL on a per-foot basis while diving, but I'm not sure since I use a bottom timer.

 

[limeyx]

Earlier you said "I haven't dived with one since dive 30 or so".

So do you dive with a computer, or not?

It's in guage mode. This means I do not use it to run my dive, calculate safety stops, NDL/Deco time etc.

I like the feature that it has to record my dive profiles so I can look at them later.

 

[limeyx]

Rather thasn spending 11 useless minutes, you and your buddy should learn how to use your tools properly. Too bad you and your buddy weren't able to catch the error during your buddy check.

Do you have any example where a properly used computer has forced anyone to dive a profile other than what you desired?

A lot of people have parroted the "doesn't give credit for deep stops" line, but if you actually look at what happens, you will find that the computer does indeed properly account for offgassing in the faster compartments.

You, at least, have not parroted the false logic about a dive computer forcing you to immediately pop up to the ceiling depth that will be shown when in deco.

I guess I need some remedial training on how to use my computer then, someone please help me!

Honestly, I dont think anything I say is going to change anything you (or probably anyone else on here) thinks, and that's fine.

I (and many others) dive my way, and other people dive theirs and I guess we leave it at that.

I think there are three threads now either going around in circles or that have degraded to name-calling. That's probably enough, I'm going back into my hole.

 

[blueeyes_austin]

Thank you for correcting blueeyes_austin's misunderstanding regarding algebra and calculus. blueeyes_austin's statement just supports my (and TS&M's) original premise that learning to use the tables or learning to use computers doesn't equate to understanding how any of those numbers were derived.

No misunderstanding. Two words: Riemann Squares, generally used in basic calculus class to give a graphical description of what integral calculus is doing (i.e., an infinitely expanding amount of infinitely decreasing squares summed together to produce the area under a curve.

That's essentially what a computer is doing...lots and lots of Rieman Squares. A human, on the other hand, even engaging in multi-level dive planning is trying to approximate the area under the curve using only a few squares.

And the computer is performing this calculation with precise knowledge of the depth of the diver at each stage of the dive...and the length of time they stay there.

The notion that a human with a simple table is going to be more precise in calculating nitrogen load is, frankly, laughable.

 

[Bobby_M]

The computer is a tool just like any other piece of gear. I mean, you could probably safely dive with only a tank and hefty bag but regulators and BCs make it a little more effecient. In a perfect world, you plan your dive on the tables beforehand just to know your worst case scenario then dive on the computer to extend your bottom time due to continuous calculation allowances. If your computer dies within your table-planned max, you may elect to spend the rest of your table-planned time using an alternate timer or abort now and make a standard safety stop. If the computer fails after that time (you're now into your computer assisted extended bottom time), abort the dive but take a bit of an extended safety stop just for added piece of mind.

There's no way that I'd prefer to plan and execute a dive on tables alone.

Bobby

 

[The Chairman]

The truly sad part? More people get bent ON computers than on tables. You would think that ANY curricula should cover how to USE these tools competently. Unfortunately, they are villified in the agencies by many who villify them here (or for the same lame-o reasons) and so students never learn the BASICS of computer diving. By denying them the education in the tools they will be using we are setting them up for failure.

But then, I am sure someone will tell them to "just read the manual". This only covers how to operate the device: not how to dive it!

 

[Charlie99]

I guess I need some remedial training on how to use my computer then, someone please help me!

No remedial training needed. But you might find it an interesting exercise to set the computer to the correct gas for your dive, and then run it as a computer while you dive whatever profile you would normally dive.

If you are diving a safe profile, the computer should be happy with that profile.

IMO there are two downsides to using a computer in the computer mode for recreational diving
1. Some divers will be lazy and rely solely upon the computer. This should not be a problem for you.
2. When displaying NDL and deco info, some computers show the depth and time in smaller numbers. Additionally, some people may be confused by the one extra number on the display.

For me, these relatively minor drawbacks are small in comparison to the benefit of having a redundant tracking of deco status to check what I'm roughly tracking mentally.

 

[Charlie99]

The truly sad part? More people get bent ON computers than on tables. You would think that ANY curricula should cover how to USE these tools competently.

For right now, let's ignore the possibility that more people get bent on computers than on tables because more people are diving computers.

The main problem I see in how some people use computers is that they are treated as infallible, black vs. white, bent vs. no bends devices. Too many people think that they are perfectly safe while diving right up to the limits of the computer/model, while in reality there is a very gradual increase in risk as one approaches and then exceed the model limits.

Related to this is the failure of most courses to teach about improved ascent procedures such as deep stops. A couple minutes spent at 40' and 30' before going to a safety stop will add significant safety margin beyond doing just a 15' stop after going right up to the no-stop limit. The 1 minute pause at half-depth that NAUI is now teaching is a significant improvement, but there is still lots of room for better teaching of how to intelligently use computers to improve dive profiles.

 

[The Chairman]

NAUI teaches deep stops from OW on now. I also emphasize that diving with a Computer should include a 5 minute OR LONGER safety stop.

Computers and tables use SWAG technology to work. They do not measure the N2 absorbed by your body. People who dive need to factor in any mitigating factors as they use their tools. This applies to tables and computers alike. There is no such thing as an "underserved hit". They might not be fully understood, but there was a reason for it happening.

 

[Charlie99]

The notion that a human with a simple table is going to be more precise in calculating nitrogen load is, frankly, laughable.

OTOH, since it is all a pretty rough approximation anyway, it is feasible to keep reasonable track of average depth and deco status in your head.

My issue with relying solely upon mental tracking is not whether it can be precise enough, or whether it is as accurate as a computer. My issue is that I am sometimes forgetful, sometimes distracted, and sometimes screw up badly in mental calculation. I prefer to keep rough track in my head, and compare that to what my computer says.