ix
SOG  Speed Over Ground, This is the ship’s relative speed to the ground. 
SPEED  The speed mainly measured by the GPS. 
STW Speed Through Water. 
Subnet mask  Value for identifying the network address 
Symbol information  Information of symbols displayed on the plotting screen.    The 
information includes symbol positions, comments, etc. 
TD  Abbreviation of Time Difference.  Time difference from the 
master-station signal of the loran system to the slave-station signal. 
Message Type 0  SBAS satellite test broadcasting. 
UTC  Abbreviation of Coordinated Universal Time.   
 
XTD alarm  This alarm informs that the own ship has got out of the scheduled 
route by the preset distance or more.