Compass Problems in Quarry? (Pearl Lake, IL)

[Dewit2it]

Not in a quarry...yet!  I have had a lot of problems with compasses up at Munising.  Diving the pillings, I've seen the compass card dipping toward the bottom with the compass level.  But it will work fine on the surface.  Also had some fun out by the Herman Hetler, and have heard reports of problems by the Selvic.  We tried doing a course at the pillings for one of Inland Seas' advanced courses and everyone got lost, so I wasn't the only one having problems there.  They stopped doing them there when even the instructor had problems.