2008 GMC Envoy Owner's Manual - Page 114

Automatic Dimming Mirror Operation The automatic dimming mirror comes on each time the ignition is turned to start. To turn the automatic dimming feature off or back on, press the on/off button. The indicator light on the mirror is lit when the automatic dimming feature is on. If after a few seconds the display does not show a compass direction, (N for North for example), there may be a strong magnetic field interfering with the compass. Such interference may be caused by a magnetic antenna mount, note pad holder, or similar object. If the letter C or CAL appears in the compass window, the compass may need to be reset or calibrated. Compass Operation Press the on/off button once to turn the compass on or off. There is a compass display in the window in the upper right corner of the mirror face. 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. Compass Calibration Press and hold the on/off button to activate the compass calibration mode. CAL will be displayed in the compass window on the mirror. The compass can be calibrated by driving the vehicle in circles at 5 mph (8 km/h) or less until the display reads a direction. 2-40