Operations Manual Perdix
Manual DocRev B
24
Average Depth
Displays the average depth of the current dive, updated once per
second. When not diving, shows the average depth of the last dive.
Average Depth in Atmospheres (AvgATM)
The average depth of the current dive, measured in absolute
atmospheres (i.e. a value of 1.0 at sea level). When not diving,
shows the average depth of the last dive.
Maximum Depth
The maximum depth of the current dive.
When not diving, displays the maximum depth of the last dive.
CNS Toxicity Percentage
Central Nervous System oxygen toxicity loading percentage.
Flashes Red when 100 or greater.
The CNS percentage is calculated continuously, even when on the
surface and turned off. When deco tissues are reset, the CNS will
also be reset.
The CNS value (short for Central Nervous System Oxygen Toxicity)
is a measure of how long you have been exposed to elevated
partial pressures of oxygen (PPO2) as a percentage of a maximum
allowable exposure. As PPO2 goes up, the maximum allowable
exposure time goes down. The table we use is from the NOAA
Diving Manual (Fourth Edition). The computer linearly interpolates
between these points and extrapolates beyond them when
necessary. Above a PPO2 of 1.65 ata, the CNS rate increases at a
fixed rate of 1% every 4 seconds.
During a dive the CNS never decreases. When back at the surface,
a half-life of elimination of 90 minutes is used. So for example, if
at the end of the dive the CNS was 80%, then 90 minutes later
it will be 40%. In 90 more minutes it will be 20%, etc. Typically
after about 6 half-life times (9 hours), everything is back close to
equilibrium (0%).
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