Buick 2001 LeSabre Owner's Manual page 118

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. Find your current location and variance zone number
on the following zone map.
2. Press and hold COMPASS (or the on/off button for
mirrors equipped with OnStar controls) until a zone
number appears in the display.
3. Once a zone number appears in the display, press
COMPASS (or the on/off button for mirrors equipped
with OnStar controls) quickly until the correct zone
number appears in the display. Stop pressing the
button and the mirror will return to normal operation.
If "C" appears in the compass window, the compass
may need calibration. See "Compass Calibration"
explained previously.
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