Clouds, fog, precipitation, wind, temperature, humidity, and other weather conditions can affect the accuracy of radar and LIDAR devices. Weather conditions can also interfere with a speed calculation based on VASCAR if conditions limit the officer's visibility of the target vehicle.

Can a radar gun be wrong?

If you know for a fact that you weren't speeding, however, you don't have to pay the ticket just because the police officer's radar gun showed that you had exceeded the speed limit. Radar guns are not infallible, and they can provide incorrect information if not operated or maintained correctly.

How often do cops have to calibrate the radar guns?

According to the operations manuals that come with police radar, to ensure accuracy, every radar unit is supposed to be calibrated with tuning forks before each and every working shift and also before and after being used to detect each speeding violation.