Teric NDL Plan

[KenGordon]

It is a perfectly good indicator so long as you don't try and redfine NDL to mean something it is not.
Yes, it is for a square profile. Like tables.
Yes, it assumes a particualar descent and ascent speed. Like tables, even computer-generated tables where you have to specify your descent and ascent speeds.

From a maths point of view it is very sensitive to the inputs making it rather unstable. On a dive a small change in depth can make a large change in NDL. Around the on/off gas limit depth it is tending towards a division by zero and so tangental. Using it as measure of risk “leave 5 minutes of NDL” is not really that helpful, that is half your nitrogen at 40m but only 10% at 20m.

 

[atdotde]

So, I am also having difficulty getting my Teric NDL plan to give me what I would find useful.
During the surface interval, I would like to know that i can, say, stay at 60 feet for, say 40minutes before i go down.
Yes, I realize that it is based theoretically on doing a square dive, which of course I am not going to do. I am going to do a gradual shallowing during the last 20minutes.
Therefore I should be WELL below that theoretical NDL limit the Teric is giving me, is that not right?

As others said, the NDL is very likely just an indicator of your fastest tissue. If you use it up at the max depth and don't want to go into deco, then that's it. But it's a different thing if you say, I leave max depth 3min before I run out of NDL and start to ascent. If you do that fast enough (of course within limits) your remaining NDL will go up once you reach shallower depths. By how much? That will also depend on you slower tissues (which by the same token clear not as fast during the surface interval.

 

[ATJ]

I think what you are really seeing here is the way the Bühlmann algorithm works. The first dive tends to have a shorter NDL compared to tables but you don't need much of a surface interval for subsequent dives.

It is easy to demonstrate in the planner by putting in repetitive dives but adjust the surface interval. You'll find after a fairly short SI, a longer SI doesn't make much difference.