Inside rearview mirror, function - GF68.49-P-2100-03T

Electro-chromatic dimming: 

The mirror lens of the inside rearview mirror (A67) can be electro-chromatically dimmed. Dimming is accomplished depending on the variables measured by the automatic dimming mirror forward sensor (A67h1) located in the mirror housing and mirror glass and the automatic dimming mirror backward sensor (A67h2) located in the mirror housing and mirror glass. This information serves also as master for the electrically adjustable and heated outside mirror (M21/1) (driver).