There is an anemometer on the tower at Balmoral underneath the flagpole. Anemometers can measure windspeed in various ways. They can drive a generator like a wind turbine would. The faster the speed, the greater the rate of flux cutting so the bigger the induced emf and thus current. You then calibrate current against known wind speeds. Another way is to have a permanent magnet spun round by the shaft so that it passes over a reed switch once a revolution. This closes a circuit and sends a pulse of current that can be counted. A similar method would involve a light passing over a detector such as an LDR once a circuit. These methods would allow calculation of angular velocity. Wind speed then = angular velocity x radius of arm,
