Anemometers are also used in mines, aviation navigation and ventilation systems. Variations of the anemometer include a three-cup and a propeller-driven design. The more quickly the wind is blowing, the faster the cups or propeller spins, providing an accurate wind speed in miles per hour, kilometers per hour or knots. In order to provide a wind direction, an anemometer must have a weather vane, and it always points in the direction from where the wind originates.
