2004 GMC Envoy Owner's Manual - Page 103

Compass Variance Compass variance is the difference between earth's magnetic north and true geographic north. The mirror is set to 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, such as during a long distance cross-country trip, it will be necessary to adjust for compass variance. If not adjusted to account for compass variance, your compass could give false readings. To adjust for compass variance, do the following: 1. Find your current location and variance zone number on the map. 2. Press and hold the on/off button for six seconds. Release the button when ZONE is displayed. The number shown is the current zone number. 3. Scroll through the zone numbers that appear in the compass/temperature window on the mirror by pressing the on/off button. Once you find your zone number, release the button. After about four seconds, the mirror will return to the compass display, and the new zone number will be set. 2-37