An anemometer is a device used for measuring wind speed, and is a common weather station instrument.
The simplest and the earliest anemometer consisted of four hemispherical cups. Later the three cup anemometer was developed which had a more constant torque and responded more quickly to gusts than the four cup anemometer.
The instrument has a cup wheel consisting of three conical cups in a horizontal plane.
The cup wheel spindle is of steel and has a connected worm gearing to a revolution counter mounted in a water proof housing.
By observing the counter reading at the beginning and at the end of any period of interval, the average wind speed during the interval can be calculated.