Davis Turbo Meter Electronic Wind Speed Indicator 
The Turbo Meter provides uncommon accuracy, sensitivity, and pocket-sized convenience. It is based on the principle that a freely turning turbine will rotate at a speed directly proportional to the wind speed. To insure maximum sensitivity and accuracy, the turbine is suspended on sapphire jewel bearings, and its rotation is sensed by an infrared light beam which adds no friction. The resulting signal is processed electronically by an LSI (Large Scale Integrated) circuit for improved reliability and reduced size. A special three digit display is used for extra resolution and provides excellent viewing contrast in bright sunlight. A handy switch selects between four different scales knots, feet per minute, meters per second, and miles per hour for unmatched versatility. Unit is compact size (2.6" x 4.7" x .7" 12cm) and light weight ( 3oz., 85g). Measures wind speed from 0 - 99.9 mph.