Furuno FAR-2807(-D) series Operator's Manual page 142

3. TARGET TRACKING (TT)
3. Push the left button to enter the reference mark.
The reference target mark (see below) appears at the cursor position and
the own ship position data label changes from "LOG," "NAV" or "MANUAL" to
"REF." Note that it takes three minutes before a new speed is displayed. If
tracking has failed for a reference target, the target is marked with a lost
target mark (symbol formed with two triangles).
4. Repeat steps 2-3 to continue entering reference marks. Three may be
entered.
Notes on speed input by reference target
• Reference targets are only used for the calculation of true speed.
• Do not use reference target generated true speed to calculate relative speed.
Relative speed data is not accurate because response to speed change is
slow, hampering the TT's ability to accurately judge the possibility of collision.
• Select a stationary target as a reference target to calculate own ship speed as
ground tracking speed. Do not choose a moving target as a reference target. A
moving target produces error in the vector for TT and AIS, which results in
wrong collision avoidance information. Further, an unstable stationary target
produces inaccurate speed data and the target itself may become lost.
• When a reference target is lost or goes out of the acquisition range, that
reference target mark blinks and the indication "REF TARGET LOST" appears
in the alarm box. If all reference targets are lost, the speed indication reads
"*.*" Select a different reference target if currently selected one is lost.
• When all targets are deleted, the reference target mark is also deleted and the
target-based speed becomes invalid. The speed is indicated as BTREF where
BT means Bottom Track (speed over ground).
• Reference targets may be marked with a vector. This can be done with 3 REF
TARGET VECTOR on the TT TARGET menu.
• Loss of reference target will affect the calculation of true speed and true
course of targets. Further, own ship speed will be inaccurate.
Canceling echo-referenced speed input
Open the SPD menu, referring to section 1.13, and set 1 SHIP SPEED to LOG,
NAV or MANUAL as appropriate.
3-4
changes to
R1
R1
Reference target
in three minutes