NDL at 18 m on air
Turn Pressure — dive planner & gas calculator
A standard reef dive: 18 m, air, an aluminium 80, thirds as the gas strategy, calm water. Here is the full plan Turn Pressure prints for it.
The figures
- NDL limit: 43 minutes (Bühlmann ZH-L16C, gradient factors 40/85, set for this example).
- Minimum gas: 40 bar (at an SCR of 20 L/min — the reserve now scales with your own breathing rate, not a fixed one).
- Turn pressure (thirds): 152 bar, reached at minute 11.4 of the dive.
- Time at maximum depth as planned: 12.14 minutes, for a total dive time of 30.99 minutes including the ascent levels and safety stop.
Inputs used
- Depth: 18 m
- Gas: air
- Cylinder: single aluminium 80 (11.1 L, 207 bar), started at 207 bar
- SAC rate: 20 L/min
- Gas strategy: thirds
- Conditions: calm
- Limit style: NDL with safety stop
- Gradient factors: 40/85 (set for this example)
The MOD line for air on this plan reads 56 m — the depth the oxygen fraction actually allows, not a number capped to the app's 40 m recreational envelope. The envelope, not the gas, is what stops the dive going deeper.
Source: Turn Pressure's pinned etalon suite, case 3 — "Standard reef dive"
(EtalonProfilesTests.swift), one of the 28 dives derived independently and
checked on every build.
Your training, your gauge and your computer decide the dive. This is pre-dive arithmetic, not a dive computer, and it does not make any dive safe.