Eliminate dangerous glare from the vehicles traveling behind you with a Gentex Automatic Dimming Rear View Mirror. The mirror detects glare and automatically dims to preserve driver vision and make night time driving safer. The brighter the glare, the darker the mirror becomes. Gentex Automatic dimming mirrors are based on the science of electrochromics, which is the process of reversibly darkening materials by applying electricity. During night time driving, the mirrors use a combination of sophisticated sensors and electronic circuitry to detect glare from rearward approaching vehicles and darken accordingly to eliminate the glare and preserve driver vision. They are popular, active crash-avoidance safety feature making night time driving safer for vehicles throughout the world. This Gentex mirror features a built-in Compass and outside Temperature display using the Path Point compass system developed by Johnson Controls. The compass is a self-calibrating flux gate compass that eliminates manual calibration by the factory, dealer or customer. It detects and compensates for compensates for actual changes in vehicle magnetics. Calibration data is stored in memory, which eliminates any requirement for recalibration after losing battery power. The electronic compass shows the direction you are heading in an easy to read digital display located above the mirror. The compass is an extremely accurate computer that displays vehicle headings of N, NW, W, SW, S, SE, E and NE. An ICE indicator will display for one minute when the temperature is at or below 37 degrees. This feature cautions you to anticipate road-icing conditions. Compass and external temperature readouts also ensure that while you are driving safer you are also driving smarter.