2006 GMC Sierra 1500 Pickup Owner's Manual - Page 156

Automatic Dimming Mirror Operation The automatic dimming mirror function is turned on automatically each time the ignition is started. To operate the automatic dimming mirror, do the following: 1. Make sure the green indicator light, located to the left of the on/off button, is lit. If it's not, press and hold the on/off button for approximately six seconds until the green light comes on, indicating that the mirror is in automatic dimming mode. 2. Turn off the automatic dimming mirror function by pressing and holding the on/off button for approximately six seconds, until the green indicator light turns off. To adjust for compass variance do the following: 1. Find your current location and variance zone number on the following zone map. Compass Variance 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 be necessary to adjust for compass variance. Compass variance is the difference between earth's magnetic north and true geographic north. If not adjusted to account for compass variance, your compass could give false readings. 2. Press and hold the on/off button until a Z and a zone number appear in the display. The compass is now in zone mode. 2-62