Repetitive dive NDL at 18 m

Same 18 m dive, same twinset, same diver — once fresh, once an hour after a 30 m dive. Turn Pressure runs the earlier dive's actual depth and time back through Bühlmann ZH-L16C rather than knocking a flat percentage off the fresh limit.

The figures

• NDL limit — fresh: 43 minutes. Repetitive: 25 minutes. Residual nitrogen from the earlier 30 m dive cuts the limit by 18 minutes.
• Minimum gas and turn pressure (halves) do not move — 40 bar and 136 bar in both cases, because the reserve is sized for an emergency ascent from maximum depth, not for nitrogen loading.
• Time at maximum depth — fresh: 42.35 minutes. Repetitive: 25.29 minutes.
• Total dive time — fresh: 125.69 minutes. Repetitive: 136.72 minutes.

The repetitive dive has less time at maximum depth but a longer total dive time. Less deep time leaves more gas unspent above the reserve, and the app spends it at 9 m rather than sending the diver up with a full-looking gauge — so a shorter NDL does not mean a shorter dive, and the app is deliberately built to show that rather than hide it.

Inputs used

• Depth: 18 m
• Gas: air
• Cylinder: twin steel 12 L (232 bar), started at 232 bar
• SAC rate: 18 L/min
• Gas strategy: halves
• Conditions: calm
• Limit style: NDL with safety stop
• Gradient factors: 40/85 (set for this example)
• Repetitive case: previous dive 30 m for 20 minutes, one hour surface interval

Source: Turn Pressure's pinned etalon suite, cases 17 ("Second dive on a twinset, short surface interval") and 18 ("First dive on the same twinset") in EtalonProfilesTests.swift — the same pair of inputs, one fresh and one repetitive.

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.