Furuno FCR-21x9-BB Operator's Manual page 304

16. NAVIGATION SENSORS
POSN (Position) page
16-4
North
cse
SOG
spd
COG
SPD
SPD:
HDG
SOG:
COG:
spd:
cse:
angle:
The sensor label (here, GPS001, GPS002) indicates the name of
the sensor.
Data Source: Check [Sensors] to use a sensor in the [Sensors] list,
or click [DR] to enter position manually. When the position source
is changed based on priorities and signal validity to another position
source, then you get the Alert 471 "Position Source Change".
DR: Check [DR] when no position source is available.
HDG
water speed
heading of ship
speed over ground
course over ground
speed of drift
course of drift
difference between HDG and COG