Chevrolet 2002 Tahoe Owner's Manual page 139

Compass Calibration
The compass may need calibration if one of the
following occurs:
D
After five seconds, the display does not show a
compass heading (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, magnetic note pad holder
or a similar magnetic item.
D
The compass does not display the correct heading
and the compass zone variance is set correctly.
In order to calibrate, the letters CAL must be displayed
in the mirror compass windows. If CAL is not
displayed, push in the COMP button for approximately
eight seconds or until the letters CAL are displayed.
The compass can be calibrated in one of two ways:
D
Drive the vehicle in circles at five mph (8 km/h) or
less until the display reads a direction, or
D
drive the vehicle on your everyday routine and after
several turns the compass will become calibrated and
will display a direction.
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 you live outside 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,
your compass could give false readings.
To adjust for compass variance:
1. Use the COMP button located at the bottom of
the mirror.
2. Press and hold the COMP button for three seconds
until a zone number appears in the display.
3. Find your current location and variance zone number
on the following zone map.
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