Chevrolet 2009 Suburban Owner's Manual page 250

To adjust for compass variance, use the following
procedure:
Compass Variance (Zone) 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
V
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.