---
title: "The first stop"
description: "Why the depth decompression begins depends on when the planner reads the ceiling, and what Committed and Continuous each do to the ascent."
---

> 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.

# The first stop

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

Leaving the bottom, your ceiling is a real depth: the shallowest the model will
let you go. Ascend towards it and it moves. The leading compartment is still
exchanging gas the whole way up, so the ceiling that sent you towards 21 m is
not the ceiling you meet when you arrive. **First Stop**, in the planner's
Decompression section, decides which of those two readings fixes the stop.

## The two settings

**Committed** reads the ceiling once, as you leave the bottom, and fixes the
stop there. You ascend to that depth and hold, whatever the ceiling has done in
the meantime. This is how MultiDeco and V-Planner cut a schedule, and how Erik
Baker described gradient factors originally. It is the default, and it is the
only setting under which GF Low governs the depth it chose.

**Continuous** re-reads the ceiling at every stop depth and lets you keep
ascending while it allows. Because the ceiling falls as inert gas comes out, you
pass the depth the bottom reading implied and begin decompressing shallower.
This is how a dive computer behaves in the water: it shows a live ceiling, and
you follow it up.

## What the choice does to a dive

Both sides plan the same dive, 45 m for 25 minutes on 21/35 with 50 % for
decompression, at the same gradient factors. Only the First Stop setting
differs.

The runtime is the same. Committed begins decompressing 6 m deeper and spends
the difference at the deep stops; Continuous carries that time to the shallow
ones. Here the setting changes the shape of the ascent, not its length.

The gap widens with the length of the free ascent. On a deep dive with a long
swim up — most of all on an open-circuit bailout, where you leave the bottom on
a helium-rich mix and the ceiling climbs before it falls — Continuous can pass
four stop depths that Committed holds.

## What it does not change

Neither setting moves the ceiling itself, and neither lets you surface before
the model allows. A dive that owes no decompression gets no stop under either.
From the first stop onwards the two are the same ascent: hold until the ceiling
rises past the next stop depth, then go up one stop.

## Next

- [Gradient factors](/theory/gradient-factors) sets the ceiling this page
  decides when to read.
- [Ascent rates](/planning/rates) sets how long the swim from the bottom takes,
  which is how far the ceiling moves before you arrive.

Source: https://docs.divelogic.ai/theory/first-stop/index.mdx