Instruments commonly used to measure wind speed are known as anemometers. They may feature a weather vane to help determine the direction of the wind.
Anemometers are commonly installed on weather stations and typically have several hemispherical cups attached to horizontal arms that rotate when contacted by wind. Other anemometers determine wind speed through the use of a propeller. The speed of the cups' or propeller's rotation determines the relative speed of the wind. Some scientific anemometers use the speed of sound to determine wind speed, air pressure and wind direction. These scientific instruments produce more precise measurements than cup and propeller anemometers.