Garmin has, in a recent GDU 4xx firmware update, changed the naming convention used for screen capture files. Instead of using what seemed to be a random number that allowed file names to be re-used (with loss of previously recorded image) they now use a date/time stamp for the name just like the data log files.

Be aware that, if the GPS has not locked, the date/time stamp used for the file name will be the time the system was "born". The GDU has no real time clock.

When doing any on ground tests that require data logging, or screen captures, it's best to ensure the GPS has lock and current time before starting the tests. This may require getting out of the hangar.