At Windmill Hill post mill, instruments on the roof of the mill constantly measure the wind speed and the rotational position of the mill relative to the prevailing wind direction. This data is fed into a microcomputer known as the Automatic Turning Device (ATD) from which control signals are sent commanding an electric motor drive to move the mill into the correct and safe position facing into the wind. High winds on the rear of the mill body could be disastrous. To guard against the dangers that could arise from mains electrical power failures all essential instrumentation and control are powered from batteries. These are kept charged from the mains.
Weather information is streamed live from a weather station mounted on the roof of the Old Bakery. At the same time a webcam gives a live feed of pictures of the mill.