Links
[1] https://www.e-navigation.nl/content/differential-gps-corrections
[2] https://www.e-navigation.nl/content/delta-differential-gps-corrections
[3] https://www.e-navigation.nl/content/gps-reference-station-parameters
[4] https://www.e-navigation.nl/content/gps-null-frame
[5] https://www.e-navigation.nl/content/gps-special-message