Furuno FEA-2807 Operator's Manual page 57

Position sensors (POSN page)
On the POSN page of the Sensors dialog
box, the data field of a position sensor
contains a label(s) that indicates the type
of the sensor. Primary-Secondary-OFF
indicates sensor status and priority. (In
the figure at right the primary sensor is
DGPS, FURUNO.) Position in local
datum, speed and course are also shown.
If a differential signal is in use with a
DGPS position the text "Diff" appears.
Position sensors have priority, indicated
by "Primary" and "Secondary". Only one
sensor can be primary while the others
can be secondary or off position. After a
sensor is turned off, its status is changed
to secondary state. When a position
sensor state is changed to primary and
another sensor was primary, the sensor
formerly primary becomes secondary.
Select the "Primary" navigation sensor as the sensor that is considered to be most accurate and reliable. Set all other
navigation sensors as "Secondary".
Kalman filter (POSN page)
The Kalman filter is an automatic process that calculates the most probable position based on position information
from all position sensors. The filter uses in its process all sensors that are not selected to OFF. See section 19.8
"Filter Operation".
Alignment (POSN page)
The position alignment is a correction given by the chart align function. It is used to move the ship to the "correct"
position. Normally turn this feature off in the start-up procedure. See section 19.9 "Position Alignment".
6. Setup Before Departure
6-7