Chevrolet 2006 Avalanche Owner's Manual page 123

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, do the following:
1. Find your current location and variance zone
number on the map.
2. Press and hold the on/off button for six seconds.
Release the button when ZONE is displayed. The
number shown is the current zone number.
3. Scroll through the zone numbers that appear in
the compass/temperature 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.
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