---
title: "Gradient factors"
description: "What GF Low and GF High do to a decompression schedule, why there are two of them, and how to read the pair you are diving."
---

> 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.

# Gradient factors

import { AlgorithmDemo } from "@/components/react/AlgorithmDemo";
import { trimixDeco } from "@/demo/plans";

A gradient factor is how much of the decompression model's allowance you are
willing to use. At 100 you ascend until your tissues sit exactly on the limit
the model draws, taking it raw with no margin. At 40 you stop 40 % of the way to
that limit and keep the remaining 60 % as margin. DiveLogic asks for two,
because the margin you want deep is not the margin you want shallow.

## The two numbers

**GF Low** governs the deepest part of the ascent. It decides how deep your
first decompression stop is. Lower it and the planner holds you deeper for
longer before letting you come up.

**GF High** governs the surface. It decides how long the shallow stops run.
Lower it and the stops at 9 m, 6 m and 3 m grow.

Between those two depths the planner slides smoothly from one to the other, so
the whole ascent is governed by a gradually tightening limit rather than a
single threshold. That is why the pair is written `40/70` and read as one
setting: neither number means much without the other. The pair is entered as
whole percentages in the **Decompression** section of the planner's Plan step.

## What the choice costs

Both sides below plan the same dive, 45 m for 25 minutes on 21/35, with 50 % for
decompression. Only the gradient factors differ.

The conservative pair buys a deeper first stop and a longer, gentler ascent. It
costs time in the water, gas, and exposure to the cold, all of which carry their
own risk. There is no setting that is only better.

- **GF Low moves the first stop; it does not add much time.** Starting the
  ascent deeper changes where decompression begins more than how long it lasts.
- **GF High is where the minutes are.** Shallow stops are where decompression
  time accumulates, so lowering GF High lengthens a dive far more than lowering
  GF Low does.

## What the pair does not tell you

A gradient factor is a fraction of one model's allowance. It is not a
probability, and `GF 70` does not mean a 70 % chance of anything.

It is also not a universal conservatism dial. The factors govern Bühlmann and
the Bühlmann half of both hybrid models. **The Thalmann models ignore the pair
completely**, and the GF fields stop having any effect when one is selected. To
compare a pair against a Thalmann schedule, see
[GF calibration](/theory/gf-solver).

They say nothing about the parts of a dive they do not govern either. Ascent
rate between stops, gas density, cold, and how hard you worked all change
outcomes without changing a single number here.

## Next

- [Tissue compartments](/theory/tissues) describes what the factors are a
  fraction *of*.
- [The first stop](/theory/first-stop) covers when the planner reads the ceiling
  GF Low draws, which decides how deep the deepest stop lands.
- [Decompression settings](/planning/decompression) is where the pair is set.

Source: https://docs.divelogic.ai/theory/gradient-factors/index.mdx