[DeepThought]

When freediving, one person could dive FRC with 2 liter of air and another can pack his lungs to 12 liter, somehow I doubt the computer is sensitive for such differences, so its algorithm should be pretty crude. I don't think scuba N2 absorption is identicle to freediving when you virtually pass over a 1000 liters in your lungs when you scuba dive.
I think heart-rate might also change loading/off-loading of N2.
Using scuba loading/off-loading algoryhtm might not work so well with freediving ascent speeds.
As far as I know the earliest scuba tables were supported by a lot of experimental data (and decomressed US navy divers), the mathematical models have improved since but I don't think they apply to freediving without any experimental data to support it.