Cylinders & gases¶

The Gas & cylinders card holds every gas the algorithm can use. Each cylinder has a role, a mix, a physical size, and a fill pressure.

Adding a cylinder¶

Tap + Add in the Gas & cylinders card. The modal opens with Bottom gas selected by default.

Fields¶

Field	What it controls
Role	How the algorithm uses the cylinder — see roles below
O₂ %	Oxygen fraction, 0–100
He %	Helium fraction, 0–95
Size (ℓ)	Cylinder internal volume in litres (e.g. 12.0 for a steel 12, 11.1 for an AL80)
Fill (bar)	Starting pressure

The mix is shown as O₂/He (e.g. 21/0 for air, 50/0 for EAN50, 16/58 for 16/58 trimix). Nitrogen is computed as 100 − O₂ − He.

Roles¶

A cylinder's role tells the algorithm when (and whether) to use it.

Bottom gas¶

The gas you breathe during the deepest portion of the dive. Used until the deeper deco gas becomes breathable on ascent.

Multiple bottom gases are allowed — the algorithm will choose the richest one within PPO₂ limits at each depth
Used for rock-bottom reserve calculation (the others are not)

Travel gas¶

An intermediate mix used to bridge the gap when your bottom gas is hypoxic at shallow depths. Typical example: 21/35 trimix to descend through the 0–30 m range before switching to a hypoxic 16/58.

Has a small reserve (configurable, default 50 bar)
Counts as an ascent-switch gas for Auto-set GF Low

Deco gas¶

A rich nitrox or oxygen mix used during decompression. Examples: 50/0, 80/0, 100/0.

The algorithm switches to the richest available deco gas as soon as its MOD is reached on ascent
Multiple deco gases stack — the algorithm progressively switches as MODs become available
Must be switched on (checkbox ✓) to be used
Counts as an ascent-switch gas for Auto-set GF Low

Bailout (CCR only)¶

OC gas carried in case of rebreather failure. Not used by the deco algorithm in normal CCR operation — only displayed for reference and gas-sufficiency checks.

Oxygen (CCR only)¶

Pure O₂ in the rebreather's O₂ cylinder, used by the loop for setpoint maintenance. Tracked for O₂ consumption and remaining duration.

Enabling / disabling gases¶

Each non-bottom cylinder has a checkbox. Only checked gases are considered by the algorithm. Use this to:

Temporarily disable a deco gas to see how the plan changes without it
Run "what-if" scenarios for missing gas at the dive site
Compare CCR bailout sufficiency with different mixes available

Bottom gases are always considered (the dive can't happen without them).

Editing a cylinder¶

Tap the cylinder row to re-open the editor. Save updates the existing entry.

Deleting¶

Tap the trash icon. If a dive segment references this cylinder, the segment is auto-healed on the next render — it gets reassigned to the first available bottom gas, and the deco recalculation triggers automatically.

Practical recommendations¶

Typical tech dive (40–60 m, OC)¶

Role	Mix	Size	Fill
Bottom	21/0 (air) or 30/30 (mod-trimix for narcosis)	2 × 12 ℓ	200 bar
Deco	50/0	11 ℓ	232 bar
Deco	100/0 (optional)	5.5 ℓ	200 bar

Heavy trimix (75 m+)¶

Role	Mix	Size	Fill
Bottom	16/58 (or similar hypoxic trimix)	2 × 16 ℓ	270 bar
Travel	21/35	11 ℓ	232 bar
Deco	50/0	11 ℓ	232 bar
Deco	100/0	5.5 ℓ	232 bar

The travel gas is what lets you set GF Low low enough to do a meaningful first deco stop without back-gas deep stops — see the Andy Davis method.

CCR¶

Role	Mix	Size	Fill
Diluent (bottom)	18/45 trimix or 21/0 — matched to depth	3 ℓ	232 bar
Oxygen	100/0	3 ℓ	200 bar
Bailout	21/35 + 50/0 + 100/0 (independent bailout)	varies	232 bar

The diluent's MOD limits your CCR maximum depth (loop PPO₂ at high setpoint must stay ≤ 1.6 even on diluent flush).

Gas density check¶

After saving cylinders, the Limits table in the Gas plan card shows gas density at the deepest segment depth. If any value goes over 5.2 g/ℓ (orange) or 6.2 g/ℓ (red), use the Best mix calculator to derive an appropriately heliumed mix.