GMC SIERRA 2002 Manual page 154

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 in the upper right
corner of the mirror face. The compass reading and the
outside temperature will both appear in the display at the
same time. The dual display can be turned on or off by
briefly pressing either the TEMP or the COMP button.
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