The six entries in the Algorithm list on the planner’s Decompression section. They are the same dive computed six ways; 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 |
| VPM-B | Not implemented. Falls back to Bühlmann. | — |
| Thalmann E-L | The US Navy exponential-linear model. Ignores gradient factors entirely. | Deeper first stop, different shape |
| Hybrid OC | Runs Bühlmann and Thalmann together and obeys whichever is stricter. | Longest of the practical choices |
| DiveLogic Frontier | Searches for schedules that trade runtime against margin, and gives you the balanced one. | Between the two models |
| 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.
VPM-B
Not implemented in this build. Selecting it computes a Bühlmann ZHL-16C schedule and says so in the warnings:
VPM-B is not yet implemented — results shown are Bühlmann ZHL-16C. Please update your algorithm selection.
The conservatism control beside it does nothing, and a schedule planned on VPM-B elsewhere is not comparable with this one.
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 stay on screen but stop affecting the schedule; Thalmann decides its ascent from its own limits.
The model runs on a Parameter Set, chosen just below it. One set is the air and nitrox one; the rest are helium sets fitted to a stated predicted incidence of decompression sickness, and a lower target incidence gives a longer schedule.
Hybrid OC
Runs Bühlmann and the selected Thalmann parameter set over the same profile and takes the deeper of the two ceilings at every point, so it is never shallower than either model would allow on its own. Expect the longest schedule of anything you would actually dive, and a warning when the two models disagree by more than 6 m.
DiveLogic Frontier
Runs both models too, but searches for schedules that trade runtime against margin and hands you the balanced one. The others it found, a fastest and a most conservative, are shown beside it on the Hybrid Analysis tab. Its risk figures are internal measures, comparable only within the one dive. See The hybrid models.
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. With the plan set to either hybrid or to GF Calibration, 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.