Posted by Chris on February 16, 2005 at 16:42:16:
In Reply to: Re: Another problem with computers posted by Kendall Raine on February 16, 2005 at 11:25:08:
All dives are based on models including those using tables, computers, depth averaging, or any other scheme. No computer yet exists with sensors on (or in) your body that can continuously monitor your body’s nitrogen absorption. Even if one existed it would also be based on a model, but a closed loop model as opposed to the open loop models that are presently used for all dives.
The algorithms that most dive computers use are much more complicated than simple depth averaging. The multi tissue compartment models use diffusion equations with different rates for each compartment. I don’t want to go into the math but it is only loosely related to depth averaging.
Depth averaging alone is described by
If it were to be converted into a finite difference equation for computer use it would be
I consider myself to be somewhat of a math whiz, but there is no way I could do either of the above equations in my head for most dives. Although it is possible to do so for very simple profiles, it is impractical and distracts from other aspects of the dive.
I don’t believe anyone who says they know their average depth for anything but a simple single or two level profile, unless they have an exact plan and stick to it. Just simple depth averaging is not simple on the fly and near impossible to do in one’s head for many dives.
Computers are a blessing to diving because they do the complicated calculations on the fly and enhance diver safety when used properly. They are not foolproof, as no system is.
In the end you need to understand the personal limitations and those of whatever system you use, and if you do and dive within those confines you stand a good chance of not getting bent. However there is no perfect model, and even individuals who everything “right” still sometimes get bent.
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