Operating Instructions
Page 27
Doc. 15301-RevB (2023-11-24)
5.1. Decompression Information
Accuracy
Decompression information displayed by this
computer, including NDL, stop depth, stop time, and
TTS are predictions� These values are continuously
recalculated and will change with changing
conditions� The accuracy of these predictions
is dependent on several assumptions made by
the decompression algorithm� It is important to
understand these assumptions to ensure accurate
decompression predictions�
It is assumed that the diver’s ascent rate is 10m/min
(33ft/min)� Ascending significantly faster or slower
than this will impact decompression obligations� It
is also assumed that the diver is carrying and plans
to use every gas that is currently turned on� Leaving
gases that are not expected to be used turned on will
result in inaccurate time to surface, decompression
stop and decompression time information being
displayed�
On ascent, it is assumed that the diver will perform
decompression stops using the gas with the highest
PPO2 below the OC Deco PPO2 value (default 1�61)�
If there is a better gas available, the current gas will
be displayed in yellow, indicating that a gas change
is expected� The decompression prediction displayed
always assumes that the best gas will be used� Even
if the switch to a better gas has not been completed
yet, decompression predictions will be displayed as if
the switch is about to occur in the next 5 seconds�
Divers can encounter longer than expected
decompression stops as well as inaccurate time to
surface predictions if they fail to switch to a better
gas when prompted by the computer�
Example: A diver on a decompression dive to
40m/131ft for 40 minutes with GF settings of 45/85
has two gases programmed into their computer and
turned on: 21% & 99%� The diver’s decompression
schedule will be calculated based on breathing 21%
oxygen for the descent, bottom and ascent phases
of the dive until the diver ascends to 6m/20ft� At
6m/20ft the PPO2 of the 99% mix is 1�606 (less than
1�61), so it is the best decompression gas available�
Decompression information for the remaining stops
will be calculated and displayed assuming the diver
is going to switch to this better gas� This dive profile
indicates these stops would be 8 minutes at 6m/20ft
and 12 minutes at 3m/10ft� If the diver never makes
the switch to 99%, the computer will not allow them
to surface until adequate off-gassing has occurred,
but it will continue to assume the diver is about to
make the gas switch and the decompression times
given will be grossly inaccurate� The 6m/20ft stop
will take 19 minutes to clear and the 3m/10ft stop
will take 38 minutes to clear� That is a total time to
surface difference of 37 minutes�
In a lost gas scenario or in the event a diver forgets
to turn off a gas they are not carrying before a dive,
gases can be turned off during the dive in Main menu
-> Edit Gases�
To Next Page
Loading...