---
title: "Decompression models"
description: "The six entries in DiveLogic's algorithm list, what each one decides, and which one is not implemented."
---

> 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.

# Decompression models

A decompression model is a set of rules for predicting how much inert gas your
tissues hold at any moment, and how shallow you may be before that loading
passes a limit the model treats as tolerable. Every schedule DiveLogic produces
is one model's answer, and different models answer differently for the same
dive.

The **Algorithm** field on the planner's Plan step offers six entries. Two are
complete models, two combine them, one translates one into the other, and one is
not implemented.

## What each entry is

| Entry | What it decides | When a diver would pick it |
|---|---|---|
| **Bühlmann ZHL-16C** | Your ceiling from tissue loading, with gradient factors setting the margin | The default, and what nearly every dive computer runs. |
| **Thalmann E-L** | Your ceiling from a fixed off-gassing assumption, with no conservatism control | Comparison and research. Its parameter sets are unverified; see the banner above. |
| **VPM-B** | Nothing. It runs Bühlmann instead | Not implemented. See below. |
| **Hybrid OC** | Runs both models and holds you at whichever ceiling is deeper | When you want the more conservative of two disagreeing models at every stop. |
| **DiveLogic Frontier** | Runs both models and produces a family of schedules from fastest to longest | When you want the trade between runtime and conservatism laid out rather than resolved. |
| **Thalmann GF Calibration** | Runs Thalmann as a reference, then reports the gradient-factor pair that comes closest to it | When you want a Thalmann result expressed in the vocabulary your dive computer uses. |

Selecting Thalmann, either hybrid, or GF Calibration also reveals a **Parameter
set** field. Read [the Thalmann page](/theory/thalmann) before relying on any of
those sets.

> **Which entries the caution covers**
>
> The unverified parameter sets named in the banner above reach **four** of the
> six entries, not one: Thalmann, both hybrid models, and GF Calibration all use
> them. Only Bühlmann and the VPM-B entry are free of them.

## VPM-B is not implemented

The list offers VPM-B and the planner does not have it. Selecting it runs
**Bühlmann ZHL-16C** and puts a warning at the top of the plan's warning list
saying so. The schedule you get is a Bühlmann schedule, and it will not show the
deep-stop profile VPM-B is known for. The **Conservatism** field that appears
alongside it, offering 0 to +5, has no effect on the schedule.

## What choosing a model does not do

Changing the algorithm changes the schedule, not the dive. Gas density, oxygen
exposure, narcosis, thermal stress and exertion are the same whichever model
produced the stops, and none of them is modelled by any of the six. A model that
returns a shorter runtime has made a different assumption, not a safer dive.

Nor is a model a probability. None of these entries returns a chance of
decompression sickness. Frontier reports a number it calls risk, which orders
schedules against each other and nothing more.

## Next

- [Bühlmann ZHL-16C](/theory/buhlmann), the default model.
- [Decompression settings](/planning/decompression), where the algorithm is set.

Source: https://docs.divelogic.ai/theory/models/index.mdx