This is straight from the manual.
This handbook describesthe Raychart 425 Chartplotter and its associated Raystar 120 GPS Receiver. The Rastar120 utilizes Satelite Differential (SD) signals for enhanced navigational accuracy over conventional shore based differential GPS systems (dGPS)
The Raystar 120GPS Reciever utilizes a new satelite differential correction system to improve the accuracy and integrity of the basic GPS signals. Three seperate compatiable systems currently exist or are being developed.
1,,,, Wide Area Augmentation System (WAAS) USA
2,,,, European geostationary Navigation Overlay System (EGNOS) European
3,,,, The MTSAT Satalite-Based Augmentation System (MSAS) Japan
The Raychart 425 Chartplotter is EGONS compatiable. However, at the time of going to print the EGNOS was still under test.
This manual was printed in March 2002,
For more info on WASS and EGNOS links can be found at www.raymarine.com
Hope this is of some help,