Chevrolet 2006 Corvette Owner's Manual page 104

Compass Variance
Compass variance is the difference between earth's
magnetic north and true geographic north. If not adjusted
to account for compass variance, the mirror's 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 you live
outside of zone eight. Under certain circumstances, as
during a long distance cross-country trip, it will also be
necessary to adjust for compass variance.
To adjust for compass variance do the following:
1. Find your current location and variance zone
number on the following zone map.
2-42
2. Press and hold the on/off button until a Z and a
zone number appears in the display. The compass
is now in zone mode.
3. Keep pressing the on/off button until the desired
zone number appears in the display. Release the
button. After approximately four seconds of inactivity,
the new zone number will be locked in and the
compass/temperature display will return.
4. Calibrate the compass as described below.