Docs → How it works
How dive matching works
Before FitDive submits a Garmin dive, it checks whether that dive is already sitting in your MySSI logbook - so a re-scanned export or a dive you logged by hand years ago doesn't get logged twice. Here's exactly how that check works, and where it can still get it wrong.
For how FitDive works out which dive site you were at (a separate kind of matching), see the Import section of Using FitDive.
Checking your logbook
Before submitting, FitDive checks the Garmin dive against two records:
- Its own memory of dives it has personally submitted or that you chose to skip.
- Your cached My SSI Logbook (Logs and Logbooks → My SSI Logbook → Sync) - so a dive you typed into MySSI by hand, years before you had FitDive, can still show up as already logged.
The second check is only as good as your last Sync there - sync your logbook first if you want a reliable historical count, e.g. before a bulk Garmin history import.
A match is decided by date/time (to the minute) and duration being close enough to survive MySSI's own seconds-free display and independent rounding on each side.
"Possible match" and the timezone problem
MySSI's logbook stores the date and time you log a dive as plain wall-clock digits - it doesn't store which timezone you were in when you entered them. Your Garmin dive computer, on the other hand, always knows its own local offset at the moment you dove. Those two clocks only actually agree if you logged the dive from the same timezone you dove in.
They can disagree by a lot: dive in Bali, then log it into MySSI a week later back home in New York, and the date/time MySSI stored is offset from what your Garmin recorded by the gap between those two zones. FitDive can't know, after the fact, which timezone you were in when you (or someone else) typed a dive in - so instead of silently treating a mismatch as "not the same dive," it widens its search to 24 hours either side and flags anything with a very close duration and depth as a possible match.
What this doesn't catch
Matching is a best-effort safety net, not a guarantee. If you share the exact same .fit file into FitDive twice, and neither its own memory nor your synced logbook already has a record close enough to flag, it will create a second entry - MySSI itself doesn't reject duplicates either. If that happens, delete the extra one from FitDive or directly in MySSI.