Leonardo da Vinci designed an anemometer, an instrument for measuring wind speed, to support his investigations of flight.
His anemometer design used a vertical plate that could move in the wind. A graduated scale indicated the force or speed of the airflow, giving Leonardo a way to record conditions relevant to flying machines and bird flight.
Leonardo studied air resistance, wind direction, and the movement of birds extensively. Those observations informed his sketches of gliders and flapping-wing machines, although none of those aircraft is known to have flown successfully.
An anemometer is not the same as a barometer. A barometer measures atmospheric pressure, while an anemometer measures wind speed. Modern anemometers commonly use cups, propellers, or ultrasonic sensors, but Leonardo's design used a much simpler mechanical arrangement.