: I just bought a stack of magnets from Lee Valley, and did some unscientific
: testing.

: Holding magnets near your monitor distorts the flow of electrons in the CRT.
: (It can also damage your monitor, so be careful). It provides a highly
: visual indication of the magnetic field.

: If all the magnets are aligned so their fields point in the same direction,
: the net magnetic field is considerable. If you all remember from science
: class, magnets have North and South poles. If you have 4 magnets and stack
: them, pointing either the North or South pole of the stack toward your
: monitor will distort the picture greatly. If you flip two magnets over so
: they are beside the other two, you have two north poles pointing up, and
: two south poles pointing up. The effect on the monitor is noticeably
: decreased.

: If you arrange all 4 magnets flat so you have a square with diagonally
: opposite magnets pointing north, and the other pair of diagonally opposite
: magnets pointing south, much of the net magnetic field is constrained
: within the area of the magnets.

: This effect decreases with distance between pairs of magnets, but is still
: significant. (even at the 3-4" spacing we see on hatch covers).

: This leads me to believe that you should flip every other pair of magnets in
: your hatch cover to minimize disturbance to nearby compasses. So, around
: the perimeter of the hatch, you'll see N-S-N-S-N-S-N-S.

: You'll still have disturbance, but probably on the order of a 4-5"
: distance instead of an 18" distance.

: Shawn

Good idea!

This could make mixing them up easy so you really have to mark the polls well.

I had one magnet poll wrong and it pushed the hatch cover out of shape with
that one pair repelling. When I noticed the problem and fixed it, the magnets
pulled the hatch cover back in shape.

Rob