Yeah I don't the idea of that because everyone's nitrogen absorption is different, so the computer may have an NDL that was calibrated by someone who absorbed nitrogen very slowly, and you do not
But that's just me.
The computer wasn't calibrated to anyone's nitrogen absorption ... that's not how computers work. It's based on a mathematical model of how an "idealized" person would absorb nitrogen at different depths and in different tissue "compartments". A compartment is theoretical tissues in your body that absorb nitrogen with certain rate ranges ... and at any given time and depth during the dive, one "compartment" or another will be the one that's closest to NDL. The "compartment" that is closest to NDL is the one that determines the computer's displayed NDL time at any given point in the dive.
Different computers use different algorithms ... which is why they will vary in showing what your NDL will be at a given time. Some are based on mathematical models for bubble formation. Others for pressure differentials (i.e. "gradients") between the air you're breathing and the pressure of the absorbed nitrogen in your tissues. Some will give you "deco" credit for deep stops while others penalize you for those same stops. None of them are based on calibrations from an actual human being. They can't be ... the rate at which your body absorbs nitrogen depends on many factors that can change from day to day, or even dive to dive. And so computer algorithms take this into account by programming a certain amount of "conservatism" into how the calculations get made. This is another reason why some computers will show you very close to deco while a different computer at the same dive profile will show that you have several minutes of NDL remaining.
In short, your dive computer knows NOTHING about you ... it only knows what the programmer told it about the ongassing/offgassing rates of a theoretical person, within the tissue "compartments" that were considered by the software.
To answer the OP's question ... I don't generally worry about NDL. On most dives, I'll try staying within it. If you go over NDL ... which is not recommended for recreational diving, but it does sometimes happen ... the key thing to remember is that your computer will give you a "ceiling" above which you may not go, and a time for which you must not go above that ceiling. Ascend at no more than the recommended rate (air supply permitting) and remain below that ceiling until your computer indicates that you have no deco obligation remaining. Unless your air supply is getting low, DO NOT proceed to that ceiling at a rapid rate, and no matter how much air you have DO NOT attempt to go back down once your computer is cleared.
In most cases, a slow ascent will clear your computer before you even reach the ceiling. If the ceiling is at 10 feet, it's best to go ahead and do your safety stop before heading to 10 feet.
There's an
article on this topic on my website that you might find useful ...
... Bob (Grateful Diver)
