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English
PDIS (Profile Dependent Intermediate Stop)
7.2 How does PDIS work?
The mathematical decompression model in Subgear XP-3G, called ZH-L8 ADT MB PMG,
tracks your decompression status by dividing your body into 8 so-called compartments and
mathematically following the uptake and release of nitrogen in each with the appropriate
laws of physics. The various compartments simulate parts of your body such as central
nervous system, muscles, bones, skin and so on.
The depth of the PDI stop is calculated as that at which the leading compartment for
the decompression calculation switches from ongassing to offgassing, and the diver is
advised to perform a 2-minute stop above the displayed depth (this is the opposite of a
decompression stop, where you are asked to remain just beneath the displayed depth).
During this intermediate stop, the body is not taking up any more nitrogen in the leading
compartment, but rather releasing nitrogen (though under a very small pressure gradient).
This, combined with the relatively high ambient pressure, inhibits bubble growth.
It should be noted that the two fastest compartments, with 5 and 10 minutes half times
respectively, are not considered for the determination of the PDI stop depth. This is due
to the fact that these compartments are only “leading” for very short dives, for which an
intermediate stop is not required at all.
NOTE:
The PDI stop is not a mandatory stop and it is NOT a substitute for the 3-5 minute
safety stop at 5m/15ft.
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