Lloyd Bonafide wrote:
You dope!

An isomagnetic map shows lines of constant magnetic field intensity.
You
need the gradient map which shows the gradient of the isomagnetic
potentials. You want the lines that go to the north pole right? Not
those
closed circles!

Hey Lloyd A Bonafide idiot,

The secular variations of the Earth's field call for frequent
determinations of the geomagnetic elements at sea. So far, general
world magnetic surveys have of necessity been restricted to the surface
of the Earth. Previous surveys, including those of the Department of
Terrestrial Magnetism of the Carnegie Institution of Washington, have
led to great improvement in our knowledge of the distribution of the
field, especially during the past few decades.

Thanks for the links BTW

Joe



"Joe" wrote in message
ups.com...
To check a compass card and compare variation values maybe.

Joe