The number which lines up with the lubber line is the boat's heading. The reading on the compass must be corrected for various factors, so don't take it literally. Variation is the difference between magnetic north and true north at a given location. Most Puget Sound skippers ignore this and do all their navigation by magnetic courses. Be advised that this would not work if you tried to do it while sailing some long distance, over which the variation changed.
Deviation is the error in the compass reading caused by magnetic sources on the boat or the crew.
It varies with the course sailed. Modern compasses have devices on them which make it possible to compensate for the magnetic sources on the boat, but even they cannot correct for some crewmember's rigging knife, and besides, neither of the club compasses are compensated at this time, although one of them could be. The club compasses are not well suited for the taking of sightings, and some club members have found it useful to carry hand bearing compasses or even backpacking compasses of their own for this purpose. Charts Charts are very symbolic representations of the surface of the earth. It helps to think of them as drawings of an infinitely magnified view of the globe, as seen from an infinite distance away, with a few corrections thrown in to deal with the fact that the earth is not flat.