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Doc. 13301-Tec-RevB (2022-05-25)
Technical Modes
Operating Instructions
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: 21/00 & 99/00� 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 99/00 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 99/00, 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�