The Decompression section sets which model computes the ascent and how much of its permitted supersaturation you use. Choosing between the models is covered in Decompression models.
Choosing the algorithm
The Algorithm card opens with a single selector; the rest of the card changes with it.
Algorithm
Both options obey the same gradient-factor ceiling. Committed fixes the first stop depth as the ascent leaves the bottom; continuous re-checks the ceiling at every stop and follows it upward, starting decompression shallower and repaying the time at the shallow stops.
| Option | What it runs |
|---|---|
| Bühlmann ZHL-16C | Bühlmann with gradient factors. The default. |
| Thalmann E-L | The Thalmann exponential-linear model, on the selected parameter set. |
| Thalmann GF Calibration | Fits a gradient-factor pair to a Thalmann schedule. |
Gradient factors
The GF pair is offered under Bühlmann ZHL-16C, entered as two whole
percentages and written as a pair: 40/70.
- Presets: three chips above the fields, Conservative (GF 30/70), Standard (GF 40/85) and Aggressive (GF 50/95). A chip highlights when the current pair matches it exactly.
- GF Low: governs the deepest stop. Lower it and the first stop moves deeper.
- GF High: governs the surfacing gradient. Lower it and the shallow stops grow, considerably faster than GF Low grows the deep ones.
A new plan starts at GF 40/70, matching none of the presets. Under Thalmann E-L the fields leave the card: that model’s conservatism is carried by its parameter set. Gradient factors covers the trade.
The other controls
- Parameter Set, for Thalmann E-L and GF Calibration: VVal-79 (Air/N₂-O₂) for air and nitrox, which a new plan uses, and a group of XVal-He sets for helium diving, each labelled with the DCS incidence it was fitted to. Those carry the caution above.
- First Stop, on every algorithm, set to Committed or Continuous: committed fixes the first stop depth as the ascent leaves the bottom; continuous re-checks the ceiling at every stop and follows it upward, starting decompression shallower and repaying the time at the shallow stops.
- Fitted GF Low and Fitted GF High, read-only, under GF Calibration: the gradient factors that reproduce the Thalmann schedule most closely. See The GF solver.
Next
Repetitive dives covers Surface Interval, the card above the algorithm when this dive follows another. Air breaks is the next page. Stop Settings, this section’s other card, is on Environment and stops.