Chevrolet 2007 Colorado Owner's Manual page 141

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, do the following:
1. Find your current location and variance
zone number on the following zone map.
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.
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