Dive Computers: What They Do and How to Choose One

A dive computer continuously measures your depth and time, then uses a decompression model (algorithm) to estimate how much nitrogen your body has absorbed. In real time it tells you how much no-decompression time you have left — no tables or mental math required.

What you'll see on the screen

• Current depth and maximum depth
• Dive time
• NDL — minutes remaining before you'd need decompression stops
• Ascent rate warning (usually an arrow or bar graph)
• Safety stop countdown
• Water temperature
• Tank pressure and gas time remaining (air-integrated models)

Features worth paying for

• Nitrox capability — essential if you dive enriched air.
• A screen you can read easily in low light and at depth.
• Simple buttons and menus you can operate with gloves on.
• Air integration via a wireless transmitter, if you like seeing tank pressure on your wrist.
• Bluetooth logging to your phone.
• Multi-gas and trimix support if you plan to move into technical diving.

Conservative vs. liberal

Different brands use different algorithms, so two computers on the same dive can show different NDLs. Most let you adjust conservatism. If you're newer, older, dehydrated, cold, or diving several days in a row, a more conservative setting is a smart choice.

Good habits

• Use your own computer for the whole day — don't swap or share mid-trip.
• Set it to the correct gas mix before every Nitrox dive.
• If your buddy's computer is more conservative, follow the more conservative one.
• Check the battery the night before your charter.
• Read the manual — then practice navigating the menus on land.