Cadillac 1999 DeVille Owner's Manual page 110

Compass Operation
Press COMPASS once 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.
If, after two 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.
Compass Calibration
If the letter "C" appears in the compass display, the
mirror may need calibration.
The mirror can be calibrated in one of two ways:
D
Drive the vehicle in circles at 5 mph (8 km/h) or less
until the display reads a direction, or
D
Drive the vehicle on your everyday routine.
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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 COMPASS button located at the bottom of
the mirror.
2. Press and hold the COMPASS button 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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