GMC 2002 Yukon XL Owner's Manual page 137

Mirrors
Inside Day/Night Rearview Mirror
Pull the tab under the mirror toward you to reduce glare
from headlamps behind you after dark. Push the tab
away from you for normal daytime operation.
Electrochromic Inside Rearview Mirror
with Compass and Temperature Display
(If Equipped)
When on, an electrochromic mirror automatically dims
to the proper level to minimize glare from lights behind
you after dark.
The mirror also includes a display of both the compass
and the temperature in the upper right corner of the
mirror face. The dual display can be turned on or off by
briefly pressing either COMP or TEMP button.
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