2008 GMC Yukon Owner's Manual - Page 149

Compass variance is the difference between earth's magnetic north and true geographic north. If not adjusted to account for compass variance, the compass could give false readings. To adjust for compass variance: 1. Find your current location and variance zone number on the following zone map. 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. Cleaning the Mirror When cleaning the mirror, use a paper towel or similar material dampened with glass cleaner. Do not spray glass cleaner directly on the mirror as that may cause the liquid cleaner to enter the mirror housing. 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. 2-51