: You MUST BE WARE the magnets will effect any compass placed in proximity.

: I found the magnets effected my compass if it came within 18” of the hatch
: cover.

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