---
title: "Algorithms"
description: "What each of the six choices in the planner's algorithm list does differently, what it costs in time, and when a diver would pick it."
---

> Documentation Index
> Fetch the complete documentation index at: https://docs.divelogic.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Algorithms

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](/theory/buhlmann)
and [Gradient factors](/theory/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.

> **These parameter sets are not verified**
>
> The parameter sets in this build were transcribed from secondary sources and
> have never been checked against the original NEDU research. They are here for
> comparison and for research, not for planning a dive you intend to make. The
> air set is additionally not a helium model, and has no validated behaviour on a
> trimix.

See [The Thalmann algorithm](/theory/thalmann).

## 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](/theory/hybrid).

## 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](/theory/gf-solver).

## 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](/theory/models) explains what these models are doing,
  rather than which to pick.
- [Every number the planner gives you](/reference/outputs) sets out what each
  choice puts on the Review step.
- [Decompression settings](/planning/decompression) is where the choice is made.

Source: https://docs.divelogic.ai/reference/algorithms/index.mdx