Chevrolet 2001 S10 Pickup Owner's Manual page 121

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.
2-50
Electrochromic Day/Night Inside Rearview
Mirror (If Equipped)
This mirror automatically changes to reduce glare from
headlamps behind you. A photocell on the back of the
mirror senses when it is becoming dark outside. Another
photocell built into the mirror surface senses when
headlamps are behind you.