Shearwater Petrel EXT, Operation Manual, Page: 42 / 65

Shearwater Research Inc. Revision 1.1.0 42
Shearwater Petrel
NDL Display
The NDL Display option allows you to display four different values
during the dive� The display can be changed during the dive to
provide different information�
Pushing SELECT will make the NDL display editable. The first
choice available will be NDL � If you select NDL, the NDL will
always be displayed during the dive whether or not you have a
decompression ceiling�
The next selection is
CEIL
� With this setting, as long as the NDL
time is 0 (you have a decompression ceiling), the raw ceiling will be
displayed instead of the NDL� This is the equivalent of the ‘Man on
a rope’� It will show your ceiling without it being rounded up to the
next even 10 foot or 3 meter stop� Please note that there is very
limited information on the effects of following a continuous ceiling
instead of stopping at stops and only moving up to the next stop
when the stop has cleared�
It is the author’s opinion that all stops should be honored� It seems
intuitive that if you have bubbles, and you stop, you give the
bubbles an opportunity to be resorbed� If you continuously ascend,
the ambient pressure is continuously reduced which prevents
bubbles from shrinking� Because of this belief, the computer will
give one MISSED DECO STOP message during the dive and one
after the dive, and will flash the stop depth and time in red as long
as you are above the stop depth� It will use the increased gradient
though, and your calculated off-gassing will be faster than staying
at the stops�
The next option is to display the actual supersaturation gradient for
a pure Bühlmann (99/99) profile.
The selection is GF99 � With this setting, as long as the NDL time is
0 (you have a decompression ceiling), the gradient will be displayed
instead of the NDL�
The number shown is the percentage of supersaturation� The
number is calculated by reference to the Ambient Pressure Line
and the M-Value line� It can be thought of as the current GF, but it is
different in a couple of ways� First, the current GF generates stops
rounded to the nearest 10 feet or 3 meters� So a gradient of 40 may
reflect a ceiling of 15 feet, but the computer will show a rounded-up
20 foot stop�
DEPTH TIME STOP TIME
DEPTH TIME STOP TIME
DEPTH TIME STOP TIME
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O
O
O
NDL Display NDL
NDL Display NDL
NDL Display CEIL
.85 .86 .84
.85 .86 .84
.85 .86 .84
DEPTH TIME STOP TIME
1.12 .98 .98
O2/HE GF99 TTS
CC 1O/5O 12 42
34.7 15 24 1
DEPTH TIME STOP TIME
Change Save
O
NDL Display GF99
.85 .86 .84