Dive education
Understanding your dive computer
A dive computer only helps you if you understand what it is telling you. This page explains, in plain language, how to use the ATMOS MISSION3 on a dive, what the different breathing gases do, what their real risks are, and how the decompression algorithm inside the MISSION3 actually works.
General dive safety education, written for MISSION3 owners and anyone curious about how a modern dive computer thinks.
Before you jump in
How to use the MISSION3 on a dive
The MISSION3 is built around three steps: set it up before the dive, read it during the dive, and log it afterwards. None of this replaces certified training; it is what that training taught you, available at a glance on your wrist.
- Before the dive: choose the dive mode that matches your dive, air, nitrox, multi-gas or gauge, and set the oxygen percentage (FO2) of the gas you will actually breathe.
- During the dive: keep an eye on depth, no-decompression limit (NDL) and ascent rate. If the MISSION3 asks for a safety stop or decompression stop, that stop is not optional.
- After the dive: give your body the surface interval the computer calculates before diving again or flying, and sync your dive to the ATMOS App to keep a digital logbook.
- Switching gas mid-dive: in Multi-Gas mode the MISSION3 tracks two gases. Only switch to the gas you have actually set up and are physically breathing, never to a gas you are not carrying.
A dive computer is an aid, not a substitute for training. Always dive within the limits of your certification level and plan every dive with a buddy.
What you breathe
The gases you dive with, and their risks
The MISSION3 supports air, nitrox and a two-gas multi-gas setup, with an oxygen fraction of up to 50 percent. It does not support helium-based trimix. Each gas changes what your body has to deal with underwater, and each comes with its own risk if it is misused.
- Air (21% oxygen): the default gas for most recreational diving. Its main risk at depth is nitrogen narcosis, a progressive, reversible impairment of judgement and coordination that gets worse the deeper you go.
- Nitrox (enriched air, more oxygen, less nitrogen): lets you absorb less nitrogen for the same dive, which can mean a longer no-decompression limit or a more conservative profile. In exchange, its maximum operating depth is shallower than air, because of the oxygen toxicity limit above. Nitrox diving requires separate certification.
- Decompression sickness (DCS, "the bends"): the risk every dive carries, air or nitrox. It happens when dissolved nitrogen comes out of solution as bubbles in tissue or blood because of too fast an ascent or too short a decompression stop. This is the risk a decompression algorithm is built to manage.
- Oxygen toxicity: breathing too high a partial pressure of oxygen, usually from diving a nitrox mix deeper than its maximum operating depth, which can cause convulsions underwater. This is why every nitrox fill is checked and every nitrox computer setting matters.
Industry-standard safe limit: the maximum partial pressure of oxygen (PO2) for recreational diving is generally set at 1.4 ATA. Exceeding it raises the risk of oxygen toxicity, regardless of which computer you dive with.
Under the hood
What a decompression algorithm actually does
Every recreational dive computer, whatever the brand, runs a mathematical model of how inert gas moves in and out of your body. The model does not measure your actual tissues; it estimates them, and it is built to stay on the cautious side of that estimate.
- Tissue compartments: the model divides the body into theoretical compartments with different half-times, from a few minutes for fast tissues like blood to several hours for slow tissues like bone and cartilage.
- Gas uptake and release: as you go deeper, each compartment absorbs inert gas toward the new pressure; as you ascend, it releases it again. Fast compartments catch up quickly, slow ones lag behind, which is why dive time and depth both matter, not just depth alone.
- Why stops and surface intervals exist: ascending, stopping, and waiting between dives all give the slower compartments time to release gas safely instead of all at once. Skipping a stop or a surface interval does not make the gas disappear, it just changes how fast it leaves your body.
Confirmed specification
The algorithm inside your MISSION3
According to the official ATMOS specification sheet, the MISSION3 runs the Bühlmann ZHL-16C decompression model with adjustable gradient factors.
- Dive modes: Air, Nitrox, Multi-Gas (two gases, oxygen up to 50%) and Gauge mode, plus dedicated freedive modes with their own logic for breath-hold diving.
- No decompression algorithm removes all risk: ascending slowly, doing your safety stop, staying hydrated and rested, and diving within your training are what actually keep the model's margins meaningful.
- Source: ATMOS MISSION3 specification sheet (M3_SPEC_B5_EN).
Bühlmann ZHL-16C, with gradient factors you can set yourself.
Gradient factors let you add a safety margin on top of the base model. A lower gradient factor means a more conservative, more cautious computer; the factory default is already set up to be safe for recreational use without any changes.
Dive prepared
Know your computer before you need it
This page is general dive safety education, not a substitute for certified training or medical advice. Always dive within the limits of your certification, get your health checked by a diving physician if in doubt, and read the MISSION3 manual before your first dive with it.