Nikon's Spot On Ballistic Wind Meter plugs directly into the headphone port found on almost all smart phones. It takes an accurate reading of the wind speed and direction and inputs the data directly into the Spot On Ballistic Match Technology Application. The Spot On app not only provides the precise aiming point on your reticle to compensate for distance, but thanks to the Spot On Wind Meter, you now can also compensate for wind drift.