Air Speed Indicator small fan anemometer by Davis Derby Ltd. designed by Busk for long distance measurements

These instruments were among the air speed indicators fitted to aeroplanes in this country. They were adapted from instruments already in use by meteorologists and mining engineers. The Wright brothers were among the first to use anemometers of this type. The instrument was fitted to a convenient strut on the aircraft. To obtain a reading the pilot pulled a string connected to the instrument for a measured time. This gave the distance flown during that period, and therefore the speed.