Jeep 2005 Wrangler Owner's Manual page 53

UNDERSTANDING THE FEATURES OF YOUR VEHICLE 53
Compass Variation Adjustment
Compass Variance is the difference between magnetic
north and geographic north. In some areas of the country,
the difference between magnetic and geographic north is
great enough to cause the compass to give false readings.
3
If this occurs, the compass variance must be set according
to the Compass Variance Map.
NOTE: When the mirror is in the VAR mode, the letter
"Z" will be displayed along with the currently selected
zone number.