Environment and stops

The Environment section and the Stop Settings card: water type, altitude, the stop grid the schedule is rounded to, and the two ppO₂ ceilings.

Water type and altitude change what a metre of depth is worth. Three further settings change the shape of the stop list the schedule is rounded onto.

Water type and altitude

The Environment section holds exactly two fields.

Salt water at sea level

Environment Settings

Water Type

Altitude (m)

Water Type: Salt Water or Fresh Water, at 1025 kg/m³ and 1000 kg/m³, which works out at 0.1005 bar per metre in salt and 0.0981 bar per metre in fresh.
Altitude (m): metres above sea level. It sets the surface pressure the whole dive is referenced to: 1.01325 bar at sea level, about 0.894 bar at 1000 m, about 0.789 bar at 2000 m.

Both feed one quantity, absolute pressure at depth, so their effects compound.

The stop grid

Three settings decide where stops may be placed and how short one may be. They live in the Decompression section, in the Stop Settings card.

Min Stop Time: 10 seconds, 30 seconds or 1 minute, starting at 1 minute. At 1 minute, a stop the model would clear in twenty seconds is still written as a full minute.
Stop Increment: 1 m through 6 m, starting at 3 m. The spacing of the grid stops are rounded to. At 3 m they fall at 3, 6, 9, 12 m; at 1 m the planner can hold you at any whole metre, for a longer stop list and a slightly shorter total.
Last Stop Depth: 3.0 m through 9.0 m in 0.5 m steps, starting at 6 m. The shallowest stop the planner will schedule; from there the diver ascends directly to the surface at the Last Stop → Surface rate. A 6 m last stop moves decompression time deeper, which costs runtime.

The two ppO₂ ceilings

Every gas is judged at every depth against two oxygen partial-pressure limits, neither editable per dive.

The bottom limit, 1.4 bar, applied at each level’s depth. Exceeding it produces a Warning naming the gas, the depth and the ppO₂ reached; the schedule still computes.
The decompression limit, 1.6 bar, the absolute ceiling. Any point in the plan where ppO₂ exceeds it produces an Error.

The per-gas ppO₂ limit set on each mix is editable, and the planner uses the stricter of the two. These are availability rules, not exposure accounting: cumulative exposure is tracked as CNS % and OTU on the Review step.

ICD safety is the last section of the Plan step: what the planner should object to when you change what you are breathing.