The button next to the slot is a master reset button. It does a hard reboot of the meter.

Opening the slots will make the button and SD card accessible but will invalidate the CATIII rating. Be safe!

The logging firmware isn’t complete yet (fighting timing bugs, sorry about that), but when it’s ready it will be released in an app/firmware update. I am putting together a cheat sheet later today because the manual question comes up frequently, but now I must run to the post office before cutoff time.