Compass Variance - GMC SIERRA 1995 Manual

Compass Variance
Under certain circumstances, as during a long distance cross-country trip, it
will be necessary to adjust the compass to compensate for cornpass
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 . Press and hold the CAL switch, located at the bottom of the mirror
housing, for five seconds until a zone number appears in the display.
2. Find your current location and variance zone number on the following
zone map.
3. Press and hold the CAL switch until the new zone number appears in
the display. After you release the switch, the display will show a
compass direction within a few seconds.
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