MyDiveLog
It reads the files from every computer you own and, when two of them recorded the same dive, makes one entry that keeps the best of each. Then it analyses your profiles and plans your dives. Your logbook lives on your device.
You wear one computer and carry a backup. You changed computer a few years ago. You download both from the manufacturer app and from the device. In all three cases the same dive ends up in two different files, and neither of them is complete. A logbook that makes you pick one makes you throw away half of what you have.
Neither entry disappears, and no data is left behind.
Two computers never agree on the time. The offset is inferred across your whole logbook, and the match is confirmed on the shape of the profile — not on the timestamp.
Between a denser profile and one that also knows about decompression, the second wins — and the first stays, because that is where rates and buoyancy are measured properly.
Every dive lists the sources it was built from. When a value is missing you know which computer never wrote it — instead of wondering whether the program lost it.
A logbook for divers who want to understand what their data is telling them, not just store it.
UDDF, Shearwater (XML and the native log), Scubapro LogTRAK, Garmin FIT, Subsurface, CSV. The format is detected from the content, not from the file extension.
Shearwater and Scubapro/Uwatec, with a bookmark: the second time round it downloads only the new dives, not the whole memory.
Bühlmann ZH-L16C with gradient factors, sixteen compartments, oxygen exposure by local day, buoyancy oscillation and ascent rates — each figure carrying its own stated reliability.
Gas and decompression: multi-level, automatic switches at the MOD, CCR with setpoint and real diluent, bailout and contingencies. Consumption comes from your own dives, not from a textbook.
Statistics, trends and suggestions with the numbers underneath: how many ascents outside the limits, how many safety stops skipped, what repetitive dives actually cost you.
Full JSON backup, UDDF export, printable logbook and dive plan. The local archive is a SQLite file you can open with any tool.
Real screenshots, taken from the app with a sample logbook: nothing retouched, and nothing the program does not actually do.
If you use more than one device, you can keep your logbook aligned. You sign in with an Apple or Google account and the app creates a database that is yours alone: there is nothing to configure, and dives travel directly between the application and that database.
Signing in is optional, and syncing is never automatic. The logbook opens, imports and analyses without ever seeing an account, because the archive is on your device. And nothing leaves until you press Sync: a logbook gets read on a boat, where there is no network.
Every person gets a database physically separate from everyone else's — not a row in a shared table. The service that hands out the keys keeps no list of users and never sees your dives: it says who you are and gives you a key that lasts two hours. You can delete your account from inside the app, and the database with it. Details in Privacy.
MyDiveLog is free software under the MIT licence: the code can be read, copied and modified. It costs nothing, has no subscriptions, no advertising, and collects no usage statistics.
The macOS package is in the releases: signed with a Developer ID and notarised by Apple, so it opens with a double click. It needs an Apple Silicon Mac.
The iPhone version runs, and it has been submitted to the App Store: meanwhile you build it from source, and the instructions are in the repository.
MyDiveLog is not a dive computer and must not be used to make decisions in the water. Its decompression calculations, plans and analyses exist to study the dives you have done and prepare the ones you are going to do: they do not replace your dive computer, your training or your judgement. Scuba diving carries risks, including death.
Free, no account and no subscription. Download it, drop in the files you already have, and a minute later your whole history is in a single list.