From PhotoVoltaic Logger new generation
If you start with PVLng and you come to a point after testing, that you must reset all measuring data in database, do it like this:
Read carefully the last point of Core section:
Enable function and save the settings.
Now the real Button to start deleting is visible.
Click to delete and ...
... confirm with another click within 8 seconds.
The option is reset afterwards automatic to No.