On light-colored wood, I make marks with a lead pencil. (.7 mm automatic pencil to be exact) The pencil line is fine enough for accuracy, is dark enough to be easily seen, and the pencil draws a long time without needing sharpening. And the pencil marks can be erased.
On dark-colored wood like walnut, the dark line of the pencil isn't as visible as I want. I've tried light-colored leads for the .7 mm pencil, but they break all the time. I've tried white chalk, but the line is way too thick. I've tried a white pencil -- the kind with cedar holding the lead -- but it needs sharpening all the time.
Anybody got a suggestion?