Why it behaves...

[RVBldr]

During a discussion at the dive site today, we're trying to understand the behavior of the Petral algorithm in this situation or a like situation (GF at medium default setting 40/85):
- Doing a deeper air dive to around 100', the NDL counts down to 0 (and it always seems to take some time to roll over to deco requirements even at depth) and we start an ascent up a slope, effectively riding the NDL at 0. It never rolls to show deco requirement.
- At about 70' the NDL reverts to maybe 12 minutes (from 0), then by about 40, it's back to 99 in a relatively short amount of time.

Is this a function of the slower tissues no longer loading? Just trying to understand the behavior.

 

[rsingler]

See this thread:
ceiling/GF

 

[rongoodman]

It probably has to do with which compartment is leading and how that changes over the course of the dive. The slower ones probably won't be taking on enough N2 to influence much on a single dive. The next time you do a similar dive, watch the tissue loading graph to get a better idea as to what's going on.