This is a re-post from an unknown source.
"An algorithm is the mathematical formula a dive computer uses that
factors in real-time measurements of depth, gas mix, time at depth - and,
depending on the algorithm, potentially lots of other data to calculate how
long you can stay underwater with a reasonable degree of assurance that you won’t
get hit with decompression sickness (DCS).
There are currently about a half-dozen different algorithms being used in
dive computers, each using its own proprietary computations, and each with its
own "liberal" or "conservative" leanings. Computers that
use more conservative algorithms lessen the risk or likelihood of DCS by
limiting dive time. Computers that use more liberal algorithms provide the
opportunity for longer dive times, but, of course, more time spent at depth
also increases the risk of DCS.
So which is the best? It really comes down to the individual diver's comfort
level. However, divers who have preconditions that might make DCS more likely
(age, poor circulation, poor physical conditioning) should always go the
conservative route. Most new computers offer methods for programming personal
safety adjustments that let you increase the conservatism of virtually any dive
The following has been added by us.
Dive computer algorithms function by calculating the “on gassing” and “off
gassing” of nitrogen in the body's tissue compartments. Each tissue layer in
the body has different rates which this gas exchange occurs; organ tissue and
light muscle tissue have much faster exchange rates than fat tissue and
dense muscle groupings. Because there are so many different tissues it is
impossible to calculate the exact rate for each person's individual tissue
layers. Because of this we operate with ranges. The U.S. Navy Tables use 6
compartments labeled as 5, 10, 20, 40, 80, and 120. These numbers correspond to
the amount of time this tissue takes to reduce the amount of nitrogen by half.
To be conservative, basic computers use only 3-4 body compartments or tissue
rates, Slow-Mid/Slow-Mid/Fast-Fast. With these four groupings a computer can
calculate how much nitrogen your body has absorbed and plan decompression accordingly.
As computers have progressed through the years and evolved, the algorithms
used have also grown and changed. Newer computers are able to calculate around
10 individual tissue rates. This allows the computer to more accurately
calculate you nitrogen levels. For example an exchange rate that might have
been lumped in with Mid/Slow but is now much more refined into
Mid/Mid/Mid/Slow. Because of this accuracy you have greater bottom time without
the risk of DCS. The added bonus to this is that your surface interval and post
dive times for off gassing will also be more accurate.
To try and stay competitive, dive computer manufacturers use different
algorithms based on different compartments, hence have different
no-decompression limits. Not saying one is better than the other, but some
divers prefer some brands over other brands.
For more information on this, feel free to call us at 281-445-3483 to
discuss the options for you.