Hummer 2005 H2 - Manual (Page 121)

In order to calibrate, CAL must be displayed in the
mirror compass windows. If CAL is not displayed, push
the COMP button for about eight seconds or until
CAL is displayed.
The compass can be calibrated by driving the vehicle in
circles at five mph (8 km/h) or less until a direction is
displayed.
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.
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 zone eight. Under certain circumstances, as
during a long distance cross-country trip, it will be
necessary to adjust for compass variance.
To adjust for compass variance, do the following:
1. Find your current location and variance zone
number on the zone map.
2. Press and hold the COMP button for five seconds
until a zone number appears in the display.
3. Press the COMP button on the bottom of the mirror
until the new zone number appears in the display.
After you stop pressing the button, the display
will show a compass direction within a few seconds.
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