The meter increases whenever the camera has the girl's privates in view. Unfortunately we ran out of time to make an in-game tutorial, but the idea would be to quickly look down to get an idea where the log would be or to follow it dropping down. Then holding right mouse button you could hold your sight steady while chopping to avoiding looking down.
We do have plans to make the girls do more than just stand around to help give a fun laid back feeling to the town.
I'll look into maybe adding some hud blush to show the character getting more flustered then more privates are in view.
Thank you for the feedback!