Learning the Mandolin fretboard

Picked up a used Mandolin (and a Tenor Guitar with GDAE tuning), so trying the same concept to learn this new (to me) fretboard.

Looks like the 9th fret marker gets moved to the 10th --- something to do with tuning in 5ths? I'll have to ask a Mandolin playing friend.

For the actual music of Mandolin, I've been taking Sierra Hull's course -- it's very newbie friendly, and she's just unbelievable!