Dodge 2008 Ram Pickup 3500 - Manual (Page 150)

Compass Variance
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. If this occurs, the compass variance must be set
using the following procedure:
NOTE: Magnetic materials should be kept away from
the overhead console. This is where the compass sensor is
located.
Compass Variance Map
150 UNDERSTANDING THE FEATURES OF YOUR VEHICLE