NavList:

I can't remember which manual I read this in. Rub the side of your nose to get some skin oil on the tip of your finger and then rub the pencil marks with tip of your finger. Try it, it works.

gl

I tried an experiment and put two pencil crosses on my Mk4B.  I rubbed one out with my right index finger moderately well.  Then I rubbed my right index finger on the side of my nose and tried rubbing out the second cross.  It definitely rubbed out better.  Then I thought “What if you were wearing an oxygen mask”, so I put a third cross on my Mk4B, rubbed my left index finger on my forehead somewhat harder, and tried that.  This also worked well.  Net result was, one smudgy mark where the first cross was, two completely disappeared crosses where the second and third were, and a slight smudge on the side of my nose.  DaveP