GMC Yukon 2007 Owner's Manual page 167

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 is
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.
Compass Calibration
The compass may need calibration if one of the
following occurs:
•
After approximately five seconds, the display
does not show a compass heading, 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, magnetic note pad
holder, or a similar magnetic item.
•
The compass does not display the correct
heading and the compass zone variance
is set correctly.
In order to calibrate, CAL must be displayed in the
mirror compass windows. If CAL is not displayed,
push the on/off button for approximately
12 seconds or until CAL is displayed.
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.
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 the
vehicle is 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, the compass could give
false readings.
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