GMC 2003 Sierra - Manual (Page 143)

In order {□ calibrate, CAL must bo displayed In the
mirror compass ift/indows. It CAL is not displayed, push
in the COMP button tor approximately eight seconds
□r until CAL is displayed.
The compass can be calibrated in one of two waysr
Drive Iho vehicle in circles at Tive itiph [B km/h)
□r less until the display reads a direction, or
* drive the vehicle on your everyday rouhne and alter
several turns Ihe compass will become calibrated
and will display a direcLon.
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 it 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 imagnel'K; north and true
geographic north, it not adjusted to account for
compass variance, your compass could give false
readings.
1. Firid your current location and variance гопе
number on the folfowing zone map.
2. Press and hold Ihe COWP button for five seconds
untlJ a zone number appears in the display.
3. Press the COMP button on the bottorn of the mirror
until Ihe new zone number appears in the display.
After you stop pressing ihe button, the display
will show a compass directioni wilWn a lew seconds.
To adjust for compass variance:
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