Descent vs. time at max depth

Time to Surface names the two legs of getting to the bottom in plain language: descent is the swim down, and time at max depth is what you do once you are there. Type one number — how long you plan to be down for in total — and the app splits it.

Worked for the reference dive

45 m for 25 minutes on 21/35:

• Descent: 4.5 minutes, at 10 m/min to 45 m — a Schreiner ramp for the tissue model, not a flat average depth.
• Time at max depth: 20.5 minutes.
• 25 minutes, total — what you typed.

Why this differs from a DecoPlanner run of the same number

DecoPlanner and GUE's own course material both count bottom time from leaving the surface, descent included — the same convention Time to Surface used until 2026-08-24. The app now separates the two legs because "bottom time" is a term two planners can mean differently, and naming both legs removes the argument over which one owns the word. Comparing this app's numbers against DecoPlanner needs descent + time at max depth against DecoPlanner's bottom time, not the typed figure against it — the same 25 minutes plans a dive about 4.5 minutes shorter at depth here than in a planner that counts the descent inside it.

The runtime clock is unaffected by this split: total runtime and every stop's runtime are still counted from the surface, which is what keeps runtimes comparable between planners.

Inputs used

• Depth: 45 m, bottom time as typed: 25 minutes
• Descent rate: 10 m/min (the app's default, adjustable)

Source: Time to Surface's pinned etalon suite, profile 07 ("The baseline") in EtalonDerivedAnswers.swift; the descent/bottom-time convention is recorded in docs/etalon-technical-profiles.md.

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.