EGNOS European Geostationary Navigation Overlay Service
GPS error is up to 56 ft. (17 m). EGNOS can reduce that to 6.6 ft. (2 m)
EGNOS, which stands for European Geostationary Navigation Overlay Service, is free to users, and the European Commission has invited manufacturers of navigation equipment to integrate EGNOS signals from satellites and ground stations into GPS units.
Proponents say basic GPS signals have a potential error of up to 56 ft. (17 m), but EGNOS can reduce that to 6.6 ft. (2 m).
More about EGNOS http://ow.ly/18mhI