What TTS is actually telling you

Posted 08 July 2026 · Field Note #26

TTS stands for time to surface: your computer's running estimate of how long it would take to get you to the surface right now, doing everything correctly — the ascent itself plus every decompression stop you currently owe. It's not a countdown you set; it's a number the computer recalculates every few seconds from your real profile.

That live quality is the whole point. Stay deep and keep loading inert gas, and TTS grows. Start ascending and off-gassing, and it generally shrinks. Watching it move tells you, in one figure, how your decompression debt is trending — whether the dive is still "cheap" to leave or getting expensive.

Below TTS, your computer also shows the schedule itself: a list of depths and times, like "6 m for 8 min, 3 m for 12 min." Read it top-down, deepest stop first — that's your shopping list for the way home. Each line is a stop you must clear before the ceiling lets you go shallower.

Here's the discipline that separates a plan from a hope: weigh TTS against your remaining gas, not just against the clock. TTS is minutes, so convert it — roughly, ascent time multiplied by your real ascent breathing rate, weighted toward the deeper, gas-hungry end. A rising TTS means a longer ascent, and at depth each breath holds more gas, so every ascent minute drains the cylinder faster. If finishing the schedule shown would eat into the reserve you set aside for emergencies, the dive is already telling you to turn around. The number isn't just information; it's a decision trigger.

The practical takeaway: glance at TTS the way you glance at your pressure gauge — as a continuous health check on the dive. Know your gas reserve cold, mentally add the gas cost of the current TTS, and turn while both still add up. Don't wait for the bottom timer to make the call for you. Decompression you can't pay for isn't decompression — it's a problem.

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⚠ Educational only — not a substitute for training or a dive computer. Verify every number independently and dive within your certification.