VASCAR (Visual Average Speed Computer And Recorder) is a type of device for calculating the speed of a moving vehicle. The first VASCAR device was created in 1966 by Arthur Marshall. It is used by police to detect speeders, without the use of traditional, detectable radar
A VASCAR unit couples a stopwatch with a simple computer. An operator records the moment that a vehicle passes two fixed objects (such as a white circle or square painted on the carriageway) that are a known distance apart. The vehicle's speed is then calculated by dividing the distance by the time.
This technique can also be used to determine a vehicle speeds from helicopters and other aerial platforms (as we see in Virginia, where they claim that your speed is checked by aircraft), making it easier to secure a conviction.
-A 1991 study by the NTSB found that VASCAR-plus units produced errors of less than 2 mph if used correctly.
Information via Wikipedia entry for "VASCAR", photo by John Morris