GMC 2008 Acadia - Manual (Page 123)

If after a few seconds the display does not show a
compass direction, (N for North for example), there may
be a strong magnetic field interfering with the compass.
Such interference may be caused by a magnetic
antenna mount, note pad holder, or similar object. If the
letter C or CAL appears in the compass window, the
compass may need to be reset or calibrated.
Compass Variance
Compass variance is the difference between earth’s
magnetic north and true geographic north. The mirror is
set to zone eight upon leaving the factory. It will be
necessary to adjust the compass to compensate
for compass variance if you live outside zone eight.
Under certain circumstances, such as during a
long distance cross-country trip, it will be necessary to
adjust for compass variance. If not adjusted to
account for compass variance, your compass could give
false readings.
To adjust for compass variance:
1. Find your current location and variance zone
number on the following zone map.
2. Press and hold the on/off button until the zone
number is displayed. The number shown is the
current zone number.
3. Scroll through the zone numbers that appear in the
window on the mirror by pressing the on/off button.
Once you find your zone number, release the button.
After about four seconds, the mirror will return to the
compass display, and the new zone number will be
set. If C or CAL appears in the compass window, the
compass may need calibration. See “Compass
Calibration” listed previously.
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