Cadillac 2008 XLR Owner's Manual page 156

Be sure to continue scanning your displays, controls
and driving environment just as you would in a vehicle
without HUD. If you never look at your instrument
panel cluster, you may not see something important,
such as a warning light. Under important warning
conditions, the CHECK GAGES message will display in
the HUD. View your Driver Information Center (DIC)
for more information.
3-34
!
+ - (Brightness): This button is used to adjust the
brightness of the HUD and the instrument panel cluster.
DIMMER: This button is used to select the HUD or
the instrument panel cluster to adjust the brightness.
HUD: This button is used to adjust the vertical position
of the HUD display.
The HUD controls are
located to the left of the
steering wheel.