Pontiac 2007 G6 Owner's Manual page 144

Compass Variance
Compass variance is the difference between earth's
magnetic north and true geographic north. If the
mirror is not adjusted for compass variance, the
compass could give false readings.
The mirror is set in zone eight upon leaving the
factory. It will be necessary to adjust the compass
to compensate for compass variance if the vehicle
is driven outside zone eight. Under certain
circumstances, such as a long distance,
cross-country trip, it will be necessary to
adjust the compass variance.
To adjust for compass variance, do the following:
1. Find your current location and variance
zone number on the zone map that follows.
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2. Press and hold the on/off button until a zone
number appears on the display.
3. Once the zone number appears on the
display, press the on/off button quickly
until you reach the correct zone number.
If C appears in the compass window,
the compass may need calibration. See
"Compass Calibration" listed previously.