Chevrolet 2007 HH7 Owner's Manual page 135

To calibrate the compass, do the following:
1. Make sure CAL is displayed. If CAL is not
displayed, press and hold the on/off button
until CAL is displayed.
2. While CAL is displayed, drive the vehicle in
circles at 5 mph (8 km/h) or less until the
display reads a direction.
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.
2. Press and hold the on/off button until a Z and
a zone number appear 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 CAL appears in the compass window,
the compass may need calibration. See
"Compass Calibration" listed previously.
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