One of the greatest inventions ever.... the flip rear view mirror inside cars.

"Except for the one Alice stepped through, most mirrors have a thin shiny layer of metal that does the reflecting, with a sheet of glass in front for structure and protection. The interior rearview mirror of most cars has an ingenious variation, in which the surface of the glass is not parallel to the mirror at the back. It is a wedge. The Guide Lamp division of General Motors worked on head and signal lights and also came up with this solution to headlight glare in the early 50s."