The Hand Anemometer is a small portable instrument that gives a direct reading of wind speed.
The instrument is held up to the wind away from obstruction. A vertical spindle with three small plastic cups rotates on ball bearings at a rate proportional to the wind speed. A permanent annular (ring-shaped) magnet is affixed to the lower end of the spindle. As the spindle rotates, the rotation of the radial magnetic field induces currents in a metal cylinder inside the body of the instrument. The resultant deflection is approximately proportional to the wind speed. The speed is indicated by the position of two red pointers against a fixed scale engraved on the transparent outer casing of the instrument.