45 m / 25 min on 21/35 with EAN50

This is the app's own reference dive — the one its documentation and test suite are built around. A sensible mid-depth technical dive: 45 m for 25 minutes on 21/35, one deco bottle of EAN50, twin steel 12s.

The schedule

• Descent: 4.5 minutes to 45 m.
• Time at maximum depth: 20.5 minutes (25 minutes bottom time minus the descent).
• First stop: 24 m, runtime 27.3 minutes.
• Stops: 24 m × 1 min, 21 m × 2 min (gas switch to EAN50), 18 m × 1 min, 15 m × 1 min, 12 m × 1 min, 9 m × 2 min, 6 m × 10 min.
• Total stop time: 18 minutes. Final ascent from 6 m: 6 minutes.
• Total runtime: 51.3 minutes, from leaving the surface to surfacing.
• CNS: 24%.

Inputs used

• Depth: 45 m, bottom time: 25 minutes (4.5 min descent + 20.5 min at depth)
• Bottom gas: 21/35 (trimix)
• Deco gas: EAN50, switch at 21 m
• Back gas: twin steel 12 L (24 L water volume, 232 bar)
• Gradient factors: 20/85 (the app's default)
• ppO₂: 1.2 bar working, 1.6 bar at a stop (the app's default)
• Descent 10 m/min, 9 m/min to the first stop, 3 m/min between stops, last 6 m at 1 m/min

Levels are arrival-to-arrival: the 24 m line's one minute is the swim up to it, not a hold there — a level printing more than one minute is genuinely held.

Source: Time to Surface's pinned etalon suite, profile 07 ("The baseline") in EtalonDerivedAnswers.swift, one of the dives listed in docs/etalon-technical-profiles.md and checked field by field against the app's own solver 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.