Pontiac 2000 Bonneville Owner's Manual page 151

Electronic Compass
The earth's magnetic field is not always the same
direction as true north as we know it. So, you must enter
a zone number to tell the compass the difference
between magnetic and actual north. This tells the
compass where in the country you are driving.
The compass remembers your zone, so you only have to
change it if you drive to a new zone on the map. The
compass adjusts only a small amount for each zone, so
you may not notice a difference if you drive from one
zone to the next one, until you cross several zones.
Some vehicles are equipped
with an electronic compass.
As with all compasses,
this unit senses the earth's
magnetic field to show
the direction the vehicle
is pointing.
Choosing Your Zone Number
Locate your zone number on the above map.
If your number is different than the one shown when
you turn the key on, follow the steps to change your
zone number.
If you live on the line, you can pick the zone area you
are most likely to drive in. (In Alaska, use Zone 9 or 10.
In Hawaii, use Zone 7).
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