DWYER® Wind Meters enable direct reading, so no calculations are required. Simply hold Meters at eye level with the back of the unit to the wind to read the low scale; then cover the finger hold for the high scale. The white ball in the tube indicates the wind speed. Meters feature two scales for maximum accuracy and easy reading—2-10 mph low scale; 4-66 mph high scale. Meters come with a pocket case and instructions. Replacement balls are available, pkg. of 3, sold separately.