Notice du Furuno GP-32

7.5 Magnetic Variation
The location of the magnetic north pole is
different from the geographical north pole.
This causes a difference between the true
and magnetic north direction. This difference
is called magnetic variation, and varies with
respect to the observation point on earth.
Your unit is preprogrammed with all the
earth’s magnetic variation. However, you may
wish to enter variation manually to refine
accuracy. Set “BRG REF” on the PLOTTER
is set to “MAG” to use magnetic variation.
1. Press the [MENU] key once or twice to
open the menu.
2. Choose PLOTTER and then press the
[ENT] key.
3. Choose MAG. VAR.
4. Press the [ENT] key.
5. Choose AUTO or MAN as appropriate
and then press the [ENT] key. For
automatic magnetic variation, current
magnetic variation appears to the right of
AUTO.
6. If you selected AUTO, no further
operation is necessary; go to step 7. For
MAN, press the [ENT] key and enter
magnetic variation as follows:
a) If necessary, change coordinate from
east to west or vice versa by pressing
▲ or ▼.
b) Press ► to shift cursor, use ▲ or ▼ to
set value, referring to a nautical chart.
c) Press the [ENT] key.
7. Press the [MENU] key twice to finish.

Ce n'est pas indiqué dans les notices des équipements ???