---
title: "Decompression settings"
description: "Choose the decompression model the plan runs on and set the gradient factors or parameter set that decides how conservative it is."
---

> 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 settings

import { AlgorithmCard } from "@/components/react/PlannerSettingsScreens";

The **Decompression** section sets which model computes the ascent and how much
of its permitted supersaturation you use. Choosing between the models is
[Decompression models](/theory/models).

## Choosing the algorithm

The **Algorithm** card opens with a single selector; the rest of the card
changes with it.

| 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. |
| **VPM-B** | Not implemented yet. See the caution below. |
| **Hybrid OC** | Both models in parallel; the deeper ceiling governs every stop. |
| **DiveLogic Frontier** | Both models across a range of conservatism settings, returning the balanced schedule. |
| **Thalmann GF Calibration** | Fits a gradient-factor pair to a Thalmann schedule. |

> **Danger**
>
> Selecting **VPM-B** does not run VPM-B. The planner falls back to Bühlmann
> ZHL-16C at whatever gradient factors are set, and warns: *"VPM-B is not yet
> implemented — results shown are Bühlmann ZHL-16C. Please update your algorithm
> selection."*

## Gradient factors

The GF pair is offered for **Bühlmann ZHL-16C** and both hybrids, 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 have no effect: that model's conservatism is
carried by its parameter set. [Gradient factors](/theory/gradient-factors)
covers the trade.

## What the other selections add

- **Parameter Set**, for Thalmann E-L, both hybrids 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.
- **Bühlmann Weight**, for both hybrids: 10 to 90 %, shown as a split,
  *70 % Bühl / 30 % Thal*. It sets how the two risk scores combine, not either
  model's ceiling.
- **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](/theory/gf-solver).

## Next

[Air breaks](/planning/air-breaks) is the next page. **Stop Settings**, this
section's other card, is on [Environment and stops](/planning/environment).

Source: https://docs.divelogic.ai/planning/decompression/index.mdx