Use a 3/4" aluminum angle as a fairing batten. The knife edge of the aluminum angle will leave black lines on all the high spots so you can use the long board to knock them down. Lew

I like that tip. I never thought to use an aluminum bar for that kind of marking.
Sounds a lot easier than trying to eyeball dips and highs, from a side viewing with a straight edge, and, then, trying to marks the spots exactly.

Sonny