Buick 2001 Century Owner's Manual page 117

There are two map lamps located on the bottom of the
mirror. Each lamp is turned on and off by pressing the
button next to the lamp.
There are also three OnStar buttons located at the
bottom of the mirror face. See your dealer for more
information on the system and how to subscribe to
OnStar. See "OnStar System" in the Index for
more information about the services OnStar provides.
Electrochromic Automatic Dimming
Rearview Mirror (If Equipped)
Your vehicle may have an electrochromic day/night
rearview mirror. Push the button in the center of the
mirror to turn this feature on. The mirror will darken
gradually to reduce glare from headlamps behind you.
This may take a few moments.
The mirror's two outer buttons operate the lights on
the bottom sides of the mirror.
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