Buick Lucerne 2007 Owner's Manual page 219

Compass Zone
Under certain circumstances, such as during a
long distance cross-country trip, it will be
necessary to compensate for compass variance
and reset the zone through the DIC.
Compass variance is the difference between the
earth's magnetic north and true geographic
north. If not adjusted to account for compass
variance, the compass in the vehicle could give
false readings.
In order to do this, the compass must be set or
calibrated to the variance zone in which the vehicle
is traveling.
To adjust for compass variance, use the following
procedure:
Compass Variance Procedure
1. Press the vehicle information button until
V
PRESS TO CHANGE COMPASS ZONE
displays.
2. Find the vehicle's current location and
variance zone number on the map.
Zones 1 through 15 are available.
219