Chevrolet 2007 Colorado Owner's Manual page 144

Compass Variance
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 outside of zone eight. Under certain
circumstances, as during a long distance
cross-country trip, it will be necessary to adjust
for compass variance. Compass variance is
the difference between earth's magnetic north and
true geographic north. If not adjusted to account
for compass variance, the compass could
give false readings.
To adjust for compass variance:
1. Find your current location and variance
zone number on the following zone map.
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2. Press and hold the on/off button until a Z and
a zone number appears in the display.
The compass is now in zone mode.
3. Keep pressing the on/off button until the
desired zone number appears in the display.
Release the button. After approximately
four seconds of inactivity, the new zone
number will be locked in and the compass/
temperature display will return.