The three entries in the Algorithm list on the planner’s Decompression section. Each computes the same dive a different way; what changes is where the model draws your ceiling, not the dive.
| Choice | What it does | Typical cost |
|---|---|---|
| Bühlmann ZHL-16C | Dissolved-gas model with gradient factors. The default, and the one every other choice is measured against. | The baseline |
| Thalmann E-L | The US Navy exponential-linear model. Takes no gradient factors. | Deeper first stop, different shape |
| Thalmann GF Calibration | Fits a gradient-factor pair to a Thalmann schedule for this dive. | Bühlmann’s cost, Thalmann’s shape |
Bühlmann ZHL-16C
Sixteen tissue compartments, each with a limit on how supersaturated it may be. Gradient factors decide how much of that limit you use: GF Low deep, GF High shallow. It is the model behind most technical dive computers, and the only choice that draws the tissue saturation map. See Bühlmann and Gradient factors.
Thalmann E-L
Tissues take gas up exponentially, as Bühlmann’s do, but give it back linearly once they are supersaturated, which moves decompression deeper and earlier in the ascent.
Gradient factors do nothing here. The GF fields leave the card when Thalmann E-L is selected; Thalmann decides its ascent from its own limits.
The model runs on a Parameter Set, chosen directly below it. One set covers air and nitrox; the rest are helium sets fitted to a stated predicted incidence of decompression sickness, and a lower target incidence gives a longer schedule.
Thalmann GF Calibration
Computes a Thalmann schedule as a reference, then finds the gradient-factor pair that most closely reproduces it in Bühlmann for this dive. You get a Bühlmann schedule, with the fitted pair shown read-only where the GF fields usually are, and a tab showing how closely the two schedules track. The pair is specific to the dive it was fitted to. See GF calibration.
What the choice does not change
- Which gas you breathe at which depth, or when a switch happens.
- Your oxygen exposure, since CNS and OTU are the same clocks under every model.
- Gas density, counterdiffusion, and every other check on the plan.
- Your ascent rates, stop grid or last stop depth.
Bailout planning runs on Bühlmann and Thalmann only. On a plan set to GF Calibration or to either hybrid, asking for bailout scenarios returns “Bailout planning supports the Bühlmann and Thalmann algorithms.” and computes nothing.
Read next
- Decompression models explains what these models are doing, rather than which to pick.
- Every number the planner gives you sets out what each choice puts on the Review step.
- Decompression settings is where the choice is made.