A wind vane is a tool used for determining the direction of the wind. Wind vanes come in different designs, but all follow the same aerodynamic design rules. They are usually placed on high locations to avoid interference in order to get accurate wind direction.
The key part on a wind vane is the pointer. It is tapered at one end to catch light winds and to provide balance. The larger part of the pointer acts as a scoop to trap the blowing wind. The weight of the device must be distributed evenly in order to function well. A wind vane is used in airports to give direction and in sailing to keep the boat on course.