Cadillac CTC 2005 Owner's Manual page 112

Compass Operation
Press the on/off button 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 current compass direction.
Compass Calibration
If after two seconds the display does not show a
compass direction, (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, note pad holder, or similar
object. If the letter C appears in the compass window,
the compass may need to be reset or calibrated.
The mirror can be calibrated by driving the vehicle in
circles at 5 mph (8 km/h) or less until the display reads
a direction.
The compass can be calibrated by pressing and holding
the on/off button until a C is shown in the compass
display.
2-42
Compass Variance
Compass variance is the difference between earth's
magnetic north and true geographic north. If the mirror
is not adjusted for compass variance, the compass
could give false readings.
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 driven
outside zone eight. Under certain circumstances, such
as a long distance, cross-country trip, it will be
necessary to adjust the compass variance.
To adjust for compass variance, do the following:
1. Find your current location and variance zone
number on the zone map that follows.