2003 Chevrolet TrailBlazer Owner's Manual - Page 119

Compass Calibration Press and hold the on/off button down for nine seconds to activate the compass calibration mode. "CAL" will be displayed in the compass window on the mirror. The mirror can be calibrated in one of two ways: D Drive the vehicle in circles at 5 mph (8 km/h) or less until the display shows "CAL," or D drive the vehicle on your everyday routine. Compass Variance (This method may take longer to calibrate). 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. 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. 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 and temperature display, and the new zone number will be set. 2-50