Another Tables vs. Computers Thread

[Rick Murchison]

computer reliability DOES NOT EQUAL safety. If your computer or bottom timer fails, you thumb the dive and make a conservative safety stop.

Well, no... if my computer fails, I continue the planned dive profile using my bottom timer; if the bottom timer fails I continue the planned dive profile using my computer
If they both fail??? I'd consider aborting the dive, depending on the circumstances, but probably wouldn't, if I could use the bottom as a depth gauge and my gas supply as my clock... I really, really hate to waste bottom time
Rick
P.S. Perhaps I should mention that when I started diving I had a single hose regulator and a watch. We measured the depth by the anchor. This kind of diving can be done safely with planning and attention; the advent of BCs, AASs, SPGs, Depth gauges, computers etc has made diving safer and put more information readily at hand to the diver if you use them, but the bottom line on safety still rests with the diver knowing what and where and how long.
--
test dozen

 

[limeyx]

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?

I dont use a computer, and have not for over 150 dives, on dives ranging from 20 feet "lobster hunting" to 150 feet tech dives. I want the flexibility to control my own profile not just during the dive, but over a range of dives. If I do a certain profile and determine that I regularly feel fatigued after it, I'm going to change that.

My tables are in my head, and I can generate a dive plan in 5 mins or less on the back of an envelope for any of the dives I do.

Say also that a different theory is presented on bottom time, ascent time etc. (a lot of agencies are now saying that a stop at 1/2 depth might be a good idea -- fancy that).

What if your computer now penalizes you for what's considered to be "best practice" because it was designed before that theory was discovered? If you rely on a computer, you probably have to buy a new one as you probably cannot update the algorithm of an existing computer (there are some exceptions)

Also, a computer can be an excuse to turn the brain off. I have seen tons of posts that go like "We did xx and yy dives, all the time keeping the computer in the green, with maybe a bit into the yellow" What the heck does that mean? What if you strapped on a less aggressive computer that "put you in the red" are you now bent when you weren't before?

Deco (and I do believe that every dive has some element of deco) is personal to all kind of things, our body, the dive conditions (how much current, effort, temperature) that to blindly follow a device that probably cannot even monitor most of those conditions seems (to me) like insanity.

Having said all that, blindly following the tables is just as bad

I think it helps to develop an understanding of what's underlying, and then you might find you need to rely less and less on what the computer is telling you.

However, this is NOT advice on how to dive, I am not a dive instructor, or dive professional in any way! Following any of my advice on diving might kill you, so please think before you dive and dont change anything on my account...

 

[minnesota01r6]

Rick, your experience and training kinda take you out of the running for taking an easy nitrox class

 

[blueeyes_austin]

Tables are algebra, dive computers are essentially performing integral calculus. I prefer the area-determining precision of calculus, while also understanding the allure of simple algebraic relationships embodied in tables.

But please don't try to pretend that a human manipulating simple dive tables prior to a dive (or even during it) is as efficient as a computer in calculating the nitrogen load from a dive profile...because we simply are not.

Another thing to consider is that, while computers can certainly introduce errors in calculation, human manipulation of tables is also a significant source for introduced errors.

In my mind, the best situation is a human who is proficient in the tables but uses at least one computer as a primary dive instrument...and monitors its readings to ensure they are reasonable. Frankly, I think diving without a computer, at least as a backup device, is simply asking for trouble.

 

[limeyx]

Tables are algebra, dive computers are essentially performing integral calculus. I prefer the area-determining precision of calculus, while also understanding the allure of simple algebraic relationships embodied in tables.

But please don't try to pretend that a human manipulating simple dive tables prior to a dive (or even during it) is as efficient as a computer in calculating the nitrogen load from a dive profile...because we simply are not.

Another thing to consider is that, while computers can certainly introduce errors in calculation, human manipulation of tables is also a significant source for introduced errors.

In my mind, the best situation is a human who is proficient in the tables but uses at least one computer as a primary dive instrument...and monitors its readings to ensure they are reasonable. Frankly, I think diving without a computer, at least as a backup device, is simply asking for trouble.

I presume you are responding to my post, and that's fine -- I would not encourage anyone to throw away their computer or tables and do it the way I do it. I think diving without a computer is asking for trouble too.

I haven't dived with one since dive 30 or so, and will not need to use one in the forseeable future (unless some radical discovery occurs).

it wasnt errors in the computations I was referring to though, it's just that every computer is an approximation of an imperfect (and often different theory). I'd rather be in control of my dive, and thankfully there are ways to do that that do not require rocket science (or a dive computer or a Phd in higher math)

 

[Charlie99]

I dont use a computer, and have not for over 150 dives, on dives ranging from 20 feet "lobster hunting" to 150 feet tech dives. I want the flexibility to control my own profile not just during the dive, but over a range of dives.

and

I'd rather be in control of my dive, and thankfully there are ways to do that that do not require rocket science (or a dive computer or a Phd in higher math)

Why do you lose control of your profile if you use a dive computer?

 

[limeyx]

and

Why do you lose control of your profile if you use a dive computer?

because you have to make the computer "happy"

an example. My buddy uses his computer as a Bottom timer (as do I -- i like the ability to download depth profiles). But he had been lazy and was running it in air mode, but we were diving 32%.

We did our dive, and on the way up, even though we were well within our minimum deco limits for 32%, his computer (because we were a bit sloppy) said 11 minutes deco. We ignored it (as it wasnt really true) and got out of the water, and he got locked out and had to borrow a bottom timer. Should I really have spent 11 useless mintues "decompressing" ?

Also, certain computers may well penalize you for doing deep stops (they calculate you are ongassing at those stops). But a lot of people believe that deep stops can help prevent bubbles expanding as you ascend. So would I rather obey the computer (which penalizes me) or have control over my profile and do the stops that I believe are safer for me?

Having said that, it's not something I would recommend anyone "just do" it takes practice and understanding and a coherent system of diving. I learned some of these concepts in my DIR-F class and honestly, it took me many months afterward to really start to get comfortable doing some of these things.

Then I took tech-1 and took the concept to a whole new level where it's possible to plan and dive (safely) a 30 minute dive at 150 feet with no computer or printed tables.

Am I saying every(any)one should just go out and do that? No, absolutely not, but if any of my comments spur even a few people to think "wow, maybe there's a better/another" way to do things and they seek out the right education, then I think that will be a good thing.

At the end of the day (in an abstract way) how other people really doesnt affect me since I have a ready supply of dive buddies who all follow the same principles.

 

[ReefHound]

My buddy uses his computer as a Bottom timer (as do I -- i like the ability to download depth profiles).

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

So do you dive with a computer, or not?

 

[DIR-Atlanta]

Tables are algebra, dive computers are essentially performing integral calculus. I prefer the area-determining precision of calculus, while also understanding the allure of simple algebraic relationships embodied in tables.

Tables and dive computers use the same basic algorithm - all modern decompression models are represented by tissue half-times, which are described by first order differential equations (i.e. equations of the form f(t) = Ae^kt). DiffEqs model many things in the natural world, from birth rates to the expiration date on your yogurt. So as far as "area-determining precision" is concerned, they are pretty much equivalent.

There are two fundamental differences between how tables operate versus how dive computers operate. First and foremost, dive computers do their calculations in "real time", while tables assume a flat profile - a dive computer will therefore give you "credit" for time spent at a shallower depth, whereas a table will not. Many people believe that this difference will always will result in more bottom time with a dive computer - this is not always true, due to the other fundamental difference.

Tables use a shorter compartment time for the so-called "controlling" compartment on repetitive dives - most computers use much longer compartments for this. For example, US Navy tables used the 120 minute compartment, where as DSAT (i.e. PADI) tables use the 60 minute compartment. Dive computers will typically use their longest compartment - perhaps something in the 480 to 720 minute range. The longer the half-time on the controlling compartment, the less bottom time you get on a repetitive dive - the effect of this is that tables generally give you more bottom time on flat profiles, whereas computers generally give you more time on multi-level profiles.

So the commonly held belief that you always get more bottom time with a dive computer is nothing more than a myth. The "optimal" tool from a dive planning standpoint therefore depends entirely on the type of dives that you are doing. Most recreational divers seem to prefer multi-level profiles, so that' s why dive computers are the planning tool of choice (at least for some).

But please don't try to pretend that a human manipulating simple dive tables prior to a dive (or even during it) is as efficient as a computer in calculating the nitrogen load from a dive profile...because we simply are not.

That all depends on how you define "efficient". To be sure, a dive computer collects its data samples with much finer granularity than a table (or a diver doing a mental approximation of a table), but there are simply too many other variables to make that level of precision meaningful in the context of inert gas loading. Not to mention the fact that most of the computer algorithms have so many hidden "fudge factors" built into them that any reasonable comparison between the two is impractical at best.

Another thing to consider is that, while computers can certainly introduce errors in calculation, human manipulation of tables is also a significant source for introduced errors.

I don't believe there is any evidence to support such an assertion. If you are aware of any, then I would be interested to see it.

In my mind, the best situation is a human who is proficient in the tables but uses at least one computer as a primary dive instrument...and monitors its readings to ensure they are reasonable.

The problem is that many divers don't do that. They use their dive computers as little more than a $300 "idiot light" - "Stay at the current depth as long as the light is green. If it turns red, ascend until it turns green again. Repeat this process until the air supply runs low, then do a safety stop (if you have sufficient gas) and surface".

In fact, I assert that a lot of divers buy computers because they are not "proficient in the tables" - they'd rather just buy a little gadget that relieves them of all the "stress" associated with using a dive table. And of course, if they cannot do tables, then have no way to determine what readings are "reasonable", because they have no basis for comparison.

Frankly, I think diving without a computer, at least as a backup device, is simply asking for trouble.

Here's a counter-argument: the more time you spend underwater, the more nitrogen you absorb (and the greater your risk of DCS). From that standpoint at least, table dives are actually safer than computer dives.

 

[The Kraken]

I guess my analogy is lost on some.

If I were to be taking a canoe trip in the deep, darkest areas of Canada, I would prefer to have an axe as opposed to a chain saw. If I lost the fuel for the chain saw, it would not work, whereas the axe would.

My mind might be mired into the educational principles of yore, but I elect to subscribe to them. That is my right and my option and, as such, is unquestionable by others.

Why?? Because it suits me to do so.

The Kraken