---
title: "Entering a gas"
description: "Add a gas in the Plan step's Gas Mixes section, read the card it produces, and give an open-circuit or rebreather plan the role it will not run without."
---

> 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.

# Entering a gas

import { GasCard } from "@/components/react/PlannerScreens";

The **Gas Mixes** section holds one **Breathing Rates** card, then one card per
gas, then an **Add Gas Mix** button. The physics behind each figure is in
[Depth limits](/gases/analysing).

## Reading a gas card

Four bands:

- **The role**, in small capitals above the mix name, with the cylinder
  configuration appended: *Deco Gas · Stage*. The edit, blend and remove
  controls sit beside it, and a **Primary** chip marks the gas breathed from
  the surface.
- **The composition**: O₂, He and N₂ as percentages.
- **The derived figures**: **MOD**, **ppO₂**, **EAD** and **Density**, plus a
  switch or drop depth where the gas has one. All are evaluated at one depth,
  named at the end of the row as *@ 45 m*.
- **The cylinder**: **Tank**, **Fill** and **Capacity**, and, once the plan is
  computed, how much you used and what is left.

A gas that breaches a limit there carries the warning on the card itself. See
[Warnings](/planning/warnings).

## Adding a gas

**Add Gas Mix** opens a five-step dialogue.
[Mixes and roles](/gases/mixes-and-roles) walks all five.

## The roles

Which roles a gas may take depends on the breathing mode.
[Mixes and roles](/gases/mixes-and-roles) lists all six and the oxygen ceiling
each carries.

Watch for:

- **An open-circuit plan needs a Bottom Gas, and a rebreather plan an Onboard
  Diluent**, or the Plan step will not advance. See
  [Warnings](/planning/warnings).
- **Changing the breathing mode does not rewrite existing roles**, so a plan
  switched to CCR reads as having no diluent.

## Next

[Cylinder configurations](/gases/cylinder-configurations) is the first thing the
builder asks for, and the setting the rest of the gas follows from.

Source: https://docs.divelogic.ai/planning/gas-mixes/index.mdx