The Dwyer WIND METER-MPH Portable Wind Meter with MPH Scale features a pocket size, sturdy plastic construction. It is ideal for yachtsmen, outdoors men, farmers, and many other users. It can be used anywhere, providing direct readings with no calculations. Simply hold the meter at eye level, with the back of the unit to the wind; a white ball in the tube will indicate wind speed. The meter has two scales for maximum accuracy and easy reading - low (2 to 10 mph range) and high (4 to 66 mph range). For high range, cover the hole with a finger.