Chevrolet 2005 Uplander Owner's Manual page 202

Compass Calibration (Uplevel Only)
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
travelling.
To adjust for compass variance, use the following
procedure:
1. Press the menu button until COMPASS ZONE
displays.
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2. Find the vehicle's current location and variance
zone number on the map.
3. Press the set/reset button to scroll through and
select the appropriate variance zone.
4. Press the menu button to advance to the
COMPASS CALIBRATION screen.
5. To start the compass calibration, press and hold the
set/reset button until CALIBRATION BEGUN DRIVE
UNTIL DONE appears in the DIC display.