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When Does a Dive Computer Start and End a Dive? Start Depth and End Delay Explained

You did one dive. Your logbook says you did two, with a three-minute "surface interval" in the middle where you swam on the surface to find the mooring line. Or the reverse: a shallow shore entry where your computer didn't seem to register the first few minutes at all.

Both come down to how your computer decides when a dive begins and ends. Most divers never look at these settings, but understanding them makes your logs cleaner, explains odd profiles, and stops a few genuinely confusing moments on dive trips.

How a computer knows you've started diving

Most dive computers wake up automatically when they get wet or when pressure rises. Some have water-contact sensors, often small metal contacts on the case, that detect immersion. Others rely only on the pressure sensor. Either way, the computer doesn't start recording a dive the instant it touches water. It waits until you pass a shallow depth threshold, and often until you've stayed there for a few seconds, so that splashing around on the surface doesn't create a log entry.

That threshold is set by the manufacturer. On some models you can adjust it, and on many you can't. The specific value is listed in your manual, and it's worth knowing roughly where it is so you understand why very shallow time isn't logged.

How it decides the dive is over

When you come back above that threshold, the computer doesn't immediately close the log. It waits to see whether you're really finished. This waiting period has different names depending on the brand: end delay, dive end time, surface time to end dive, or similar.

• If you go back down before the delay runs out, the computer continues the same dive.
• If you stay on the surface longer than the delay, the dive is closed and the next descent starts a new one.

Some computers let you change this delay. Others fix it. A few show a countdown on the surface so you can see when the dive will be closed.

Why one dive becomes two (and why it matters)

The classic case is a mid-dive surface swim. You come up to check your position, swim on the surface to the reef, and drop back down. If the end delay is short, the computer closes the first dive and starts a second. Your logbook now shows two short dives with a brief interval between them.

Other common situations:

Does the split matter for safety? On most computers, the decompression model keeps tracking your tissue loading continuously whether or not the log is split, because it's following measured pressure over time, not the logbook entries. The split mostly affects how your dive appears in the logbook and app. That said, implementations vary, so confirm how your model behaves in its manual.

Choosing an end-delay setting

If your computer lets you adjust it, think about the diving you do most:

A longer delay has one practical downside: on many computers, some menus and settings are locked while a dive is "in progress". If you want to change something right after surfacing, you'll need to wait for the dive to close first.

The start-depth threshold and shallow diving

Very shallow diving, such as a confined-water session, a seagrass survey or a shallow shore dive with long stretches near the surface, can confuse logs. The computer may not start until you go a little deeper, or may close the dive if you spend a long time near the threshold.

If you do a lot of shallow diving, check:

• Whether the start threshold is adjustable on your model.
• Whether shallow time is still recorded in the profile even if it doesn't count as part of the dive.
• Whether there's a specific mode for shallow or training dives.
• How your app displays very short dives, and whether you can merge or hide them.

Fixing split logs after the fact

Many logbook apps and desktop programs let you merge two dives into one or delete accidental short dives. Some only let you hide them. Before you merge anything, remember that the original data is your record. If you might need it later, for instance for a certification log or an incident report, keep the original export.

1. Export or sync the raw data first so you have an untouched copy.
2. Check your app's merge or combine feature, usually in the dive detail or edit view.
3. Add a note explaining that the dive was merged and why.
4. Adjust your end-delay setting if this keeps happening.

For more on logging workflows, see our guides on logging dives with your computer and app and Bluetooth vs USB data export.

Other settings that affect when the computer wakes

Water-contact sensors and wet contacts

If your computer uses water-contact sensors, a damp gear bag or a rinse tank can wake it. On some models this is harmless; on others it can drain the battery if it keeps waking. Dry the contacts before storing it, and use a case that keeps it from sitting in water.

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Altitude and surface pressure

The computer measures surface pressure before the dive and uses it as a baseline. If you drive up to a mountain lake and dive immediately, or switch the computer on in a pressurized aircraft cabin, that baseline matters. Read our guide to altitude diving basics and follow your manual's instructions for altitude.

Sleep and power-saving modes

Some computers go into a deeper sleep after long periods without use and may take longer to wake. If you're unsure, turn it on manually before the dive and check that it's showing the expected mode.

Gear that helps on shallow and shore dives

If surface swims are what's splitting your logs, the gear that makes them easier also makes the dive more pleasant: a visible surface marker, a snorkel you can stow, and a reliable compass for the swim out.

Shop surface marker buoys Browse foldable snorkels Browse wrist compasses