Make Nighttime Driving Safer! Eliminate dangerous headlamp glare from the vehicles traveling behind you with a Gentex automatic-dimming rearview mirror. It detects glare and automatically dims to preserve driver vision and make nighttime driving safer. The Gentex 20a also offers a compass and a temperature display. New dual display simultaneously shows vehicle's heading and outside temperature. ICE indicator displays for one minute when the temperature is at or below 37 degrees, helping you anticipate road-icing conditions.