"Terry Spragg" wrote in message
...
Evan Gatehouse wrote:


First I ever heard of such a thing.

I can't believe it matters. A compass is a compass.

It is because the Earth's magnetic field is not spherical. It dips in as
you get closer to the poles. Compass cards are not accurate unless they are
level. From about lat 35 to 40 on up to the poles the needle tends to dip
downward as it tries to align itself with the magnetic flux. Good compass
cards are balanced to counteract this dip. When a compass set up for the
Northern hemisphere is in the Southern hemisphere the counterweight
accentuates the dip and vise versa..