GMC 2000 Sierra - Manual (Page 134)

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Compass Operation
Press the COMP switch once briefly to turn the compass
on or off.
When the ignition and the compass feature are on, the
compass will show two character boxes for
approximately two seconds. After two seconds, the
mirror will display the compass heading.
When cleaning the mirror, use a paper towel or similar
material dampened with glass cleaner. Do not spray
glass cleaner directly on the mirror as that may cause the
liquid cleaner to enter the mirror housing.
Compass Calibration
The compass may need calibration if:
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 letter “C” must be displayed in
the mirror compass windows. If “C” is not displayed,
push in the “COMP” button for approximately eight
seconds or until the letter “C” is 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 compass 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.