Short guides to the technology divers use every day. They explain how things work; your training, your dive computer's manual and your instructor come first.
Dive computer basics
Your dive computer tracks your depth and time and uses a decompression model to estimate how much nitrogen your body has taken on. From that, it shows a few numbers that matter most:
No-decompression limit (NDL). How many more minutes you can stay at your current depth and still ascend directly to the surface, with a safety stop.
Ascent rate. Most computers warn you if you come up too fast. Slow ascents are one of the simplest safety habits.
Safety stop. Many computers count down a stop near 15 feet at the end of a dive.
Gas. If you dive nitrox, your computer needs the right oxygen percentage set before the dive.
Surface interval and no-fly time. After a dive, many computers show time since surfacing and how long to wait before flying.
Every computer is different. Read your manual, and practice with your settings on easy dives first.
Gradient factors, explained
Many computers, including Shearwater and Garmin dive computers, use a decompression model called Bühlmann. Gradient factors are two percentages that make that model more or less conservative.
GF high sets how close to the model's limit you can be when you reach the surface. For most recreational diving, this is the number that matters most. A lower GF high means shorter no-deco times and more margin.
GF low mainly shapes deeper stops on dives that need decompression, so it rarely affects typical recreational dives.
Settings like "low, medium, high" conservatism are usually preset gradient factor pairs.
No setting guarantees safety; decompression sickness can happen inside a computer's limits. If you're unsure which setting to use, choose the more conservative one and ask your instructor.
With air integration, a small transmitter screws into your regulator's first stage and sends your tank pressure wirelessly to your dive computer. The computer can then show your pressure, your gas use and an estimate of time remaining.
The transmitter has to be paired with your computer and has its own battery.
Signals can drop out briefly, especially when another diver's transmitter is close by.
Many divers also keep an analog pressure gauge as a backup.
Your dive data files
Dive computers and apps save your dives in different file types. Knowing which one you have makes it easier to move your log where you want it.
Format
What it is
Where you'll see it
UDDF
Universal Dive Data Format: an open format that many dive log programs can read and write.
Exports from Shearwater Cloud and other apps. The DiveFolk Logbook reads it.
DL7
The dive log format from DAN (Divers Alert Network). Files end in .zxu.
Some dive apps export and import it.
CSV
A plain spreadsheet file: rows and columns of text.
Opens in Excel, Google Sheets, Numbers and almost anything else.
FIT
Garmin's activity file format.
Garmin dive computers and watches. The DiveFolk Logbook reads it.
Shearwater .db
The database file Shearwater Cloud keeps on your computer, holding all your dives.
Shearwater Cloud's File menu, under Export Database.
Back up your dive log
A dive log is hard to rebuild if you lose it. A simple routine keeps it safe:
After each trip, export your dives from your dive computer's app (UDDF and CSV are good choices).
Keep everything in one folder you own: your spreadsheet, the computer files and photos of your paper logbook pages.
Keep a second copy somewhere else, such as a cloud drive or an external drive.
An app that syncs to the cloud is convenient, but it's not the same as a copy you control.
