GMC 2010 Sierra 1500 Crew Cab Owner's Manual page 288

To adjust for compass variance, use the following
procedure:
1. Do not set the compass zone when the vehicle is
moving. Only set it when the vehicle is in P (Park).
Press the vehicle information button until
PRESS TO CHANGE COMPASS ZONE
displays. Or, if the vehicle does not have DIC
buttons, press the trip odometer reset stem
until CHANGE COMPASS ZONE displays.
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2. Find the vehicle's current location and variance
zone number on the map.
Zones 1 through 15 are available.
3. Press the set/reset button to scroll through and
select the appropriate variance zone.