62
LUNA 2.0 AI USER MANUAL
3 .15 PDIS (Prole-Dependent Intermediate Stops)
3 .15 .1 Introduction to PDIS
The main purpose of a dive computer is to track your nitrogen uptake and recommend a safe ascent procedure.
Diving within the so-called no-stop limits means that at the end of the dive you can ascend directly to the surface,
albeit at a safe ascent rate, while for dives outside of the no-stop limit (so-called decompression dives), you must
perform stops at certain depths and allow time for excess nitrogen to be expelled from your body before nishing
the dive and re-surfacing.
In both cases, it can be benecial to stop for a few minutes at an intermediate depth between the maximum depth
attained during the dive and the surface or, in case of a decompression dive, the rst (deepest) decompression
stop.
An intermediate stop of this kind is benecial as soon as the ambient pressure at that depth is low enough to
ensure that your body is predominantly off-gassing nitrogen, even if under a very small pressure gradient. In such
a situation, you can still cruise along the reef and enjoy the dive while your body gets a chance to slowly release
nitrogen.
In recent times, so-called “deep” stops have been introduced in some dive computers and tables, dened as half
the distance from the dive’s maximum depth and the surface (or the lowest decompression stop). Spending 2 or
15 minutes at 30m/100ft would result in the same deep stop at 15m/50ft.
With PDIS, as the name suggests, the LUNA 2.0 AI interprets your dive prole and suggests an intermediate
stop that is a function of your nitrogen uptake so far. The PDI stop will therefore change over the course of the
dive to reect the continuously changing situation in your body. Along the same lines, PDIS will account for the
accumulated nitrogen from previous dives; hence, PDIS is also repetitive-dive dependent. Conventional deep stops
completely ignore these facts.
The following gure quanties the extent of PDIS and illustrates its dependence on cumulative nitrogen uptake
for 2 sample dive proles. This gure also demonstrates the conceptual difference between PDIS and the rather
rudimentary “deep” stops. Specically, the gure compares 2 dive
proles to a maximum depth of 40m/132ft that are otherwise very different.
Prole 1 stays at 40m/132ft for 7 minutes, then ascends to 30m/100ft for 3 minutes, followed by 12 minutes
at 20m/65ft. Prole 2 stays less than 2 minutes at 40m/132ft, then ascends to 21m/69ft and stays there for 33
minutes. Both dive proles are no-stop dives to the limit of entering decompression.
The solid line represents the PDIS depth as displayed on the computer screen during the course of the dive for
prole 1, the broken line represents the PDIS depth as displayed on the computer screen during the course of
prole 2. One can see that the displayed PDIS depth increases as more nitrogen is accumulated in the body but
does so very differently in the 2 dives due to the different exposure in the 2 proles. The PDI stop is carried out at
25 minutes for prole 1 and at 37 minutes for prole 2, followed by the safety stop at 5m/15ft.
The line made up of small solid dots, on the other hand, represents the depth that would be displayed by a
computer following the conventional deep stop method, and it would be the same for the 2 dive proles. Deep
stops completely ignore any facts about the dives themselves aside from max depth.
To Next Page
Loading...
Need help?
General
