Chevrolet 2002 Corvette Owner's Manual page 176

If the sun comes out or it becomes cloudy, you may
need to adjust the HUD brightness again using the
dimmer control. Polarized sunglasses could make the
HUD image harder to see.
To change from English to metric units, push the
E/M button located to the right of the steering wheel.
Clean the inside of the windshield as needed to remove
any dirt or film that reduces the sharpness or clarity of
the HUD image.
To clean the HUD, spray household glass cleaner on a
soft, clean cloth. Wipe the HUD lens gently, then dry it.
Do not spray cleaner directly on the lens because the
cleaner could leak into the unit.
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If the ignition is on and you can't see the HUD image,
check to see if:
D
Something is covering the HUD unit.
D
The HUD dimmer control is adjusted properly.
D
The HUD image is adjusted to the proper height.
D
Ambient light (in the direction your vehicle is
facing) is low.
D
A fuse is blown. See "Fuses and Circuit Breakers"
in the Index.
Keep in mind that your windshield is part of the HUD
system. If you ever have to have your windshield
replaced, be sure to get one that is designed for HUD or
your HUD image may look blurred and out of focus.