Anemometer: an instrument which measures wind speed or wind speed and direction. A cup anemometer is used to measure the wind speed from the speed of rotation of a windmill which consist of 3 or 4 hemispherical or conical cups, each fixed to the ends of horizontal arms attached to a vertical axis. A byram anemometer is a variety of the cup anemometer. A counting anemometer has cups or a fan whose rotation is transmitted to a technical counter which integrates directly the air movement speed. A hand anemometer is a small portable anemometer held at armâ€™s length by an observer making a wind speed measurement. A pressure tube anemometer (Dines anemometer) is an instrument which derives wind speed from measurements of the dynamic wind pressures. Wind blowing into a tube develops a pressure greater than the static pressure, while wind blowing across a tube develops a pressure less than the static. This pressure difference is proportional to the square of the wind speed.