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From: <Deep1dave@ao*.co*>
Date: Tue, 13 Jun 2000 16:49:44 EDT
Subject: Deco diving: Dive Computers vs. Bottom Timers
To: techdiver@aquanaut.com

Greeting list,

Lately there has been a lot of posts regarding computers Vs bottom timers for 
deco.  I found a good summary that was posted by Jarrod Jablonski last 
February.  

I have recently switched to diving with decoplanner tables, and a bottom 
timer.  At first, it was awkward to have to look at a table during deco.  Now 
I have many of our  typical profiles with the appropriate mixes memorized, 
and my deco doesn't depend on a computer.  Even if I loose my slate, I can do 
the deco.  

During my normoxic trimix class, I dove with both a 2 gas Cochran Commander, 
and a bottom timer with tables.  I wanted to see what the Cochran would do 
since it only new about the 50% switch at 70fsw.  Well, on shallow dives, say 
to 160fsw for 20min, the cochran would clear at about the time the table had 
me out of the water.  However, on the 200fsw for 20min dive, the Cochran 
would bend it self, and lock me out, at the 20fsw stop.  In addition, on one 
of the dives, the Cochran really went south and gave me a ceiling of 20fsw 
when I actually hadn't completed my 50fsw stop.  That's when I really became 
convinced that we can't safely deco on dive computers.

Deep diving is not a "by the seat of the pants" event.  One is forced to plan 
the dive for gas consumption and deco.  Understanding and familiarizing your 
self with your deco is just part of it.

Below is the post of Jarrod's. 

Hope it helps,

Dave



" 1) Dive computers tend to induce significant levels of diver dependance, 
eliminating the awareness so common and essential to all diving but 
particularly obvious when diving tables

2) Dive computers do not allow proper planning as divers can't properly 
"study" the impact of various mixture and decompression choices.

3) Dive computers are of very limited educational benefit as they do not 
induce questioning, or proper planning discussions as can be found with 
tables and most particularly with deco programs

4) Dive computer programmers often play games with computational process so 
that they can take insulate themselves from the risk of taking largely 
square profile data and utilizing it on a multilevel dive. These games tend 
to result in odd and often ridiculous levels of conservation.

5) Dive computers are expensive and in some cases leave divers with limited 
resources carrying equipment that is of far less benefit than other 
equipment that may have been purchased.

6) Dive computers significantly limit the likelihood that divers will track 
their residual nitrogen groups.

7) Dive computers do not allow for Helium diving in any formats but the 
bulkiest and most questionable format.

8) Dive computers will often generate longer decompressions than could be 
figured by an astute, well educated diver with experience.

9) Dive computers often create confusion by giving the user to much useless 
information, sometimes even obscuring depth and time in favor of blinking 
CNS and/or deco limitations.

10) Dive computers can become very difficult to properly if a deco stop has 
been violated. Some computers lock up completely while others just beep or 
generate erroneous and distracting information. Divers using mixed gasses 
are likely to often violate computer profiles.

11) Dive computers do not allow for the educated diver to properly modify 
their decompression to account for advancing knowledge such as the use of 
deeper stops in a decompression profile.

12) Dive computers do not offer divers as much flexibility in the 
generation of profiles with varying conservation. For example the right mix 
would allow 100 min at 60 vs 60 at 60 but I might prefer to do one or the 
other and indeed might like a compromise. Computers confuse this issue by 
not providing divers with the proper information.

13) Dive computers users often ignore table proficiency and therefore do 
not learn tables properly. When confronted with a situation where they 
can't dive the computer (failure, loss, travel etc) these divers are at a 
serious handicap.
Jarrod Jablonski

President-
Global Underwater Explorers www.gue.com
CEO Extreme Exposure www.extreme-exposure.com
VP Halcyon Manufacturing www.halcyon.net, www.browniedive.com, 
www.tankfill.com"

Global Underwater Explorers www.gue.com
GUE is a non-profit educational, research, and exploratory organization 
with hundreds of dedicated members around the world.

Extreme Exposure www.extreme-exposure.com
Extreme Exposure and Halcyon manufacturing produce some of the scuba 
industries most novel and robust diving equipment designed by many of 
diving's most active explorers.
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