Furuno FAR-28x7 Series Operator's Manual page 130

3. ARP OPERATION
4. Push the left button to enter the reference mark. (The mark may also be
entered by pressing the [ENTER MARK] key on the full keyboard.)
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 60 scans or approximately 1 min 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).
5. Repeat steps 2-4 to continue entering reference marks. Three may be
entered.
Notes on speed input by reference target
• When the reference target is lost or goes out of the acquisition range, the
reference target mark blinks and the speed reads "*.*" Select a different
reference target in this case.
• When all targets are deleted, the reference target mark is also deleted and the
target-based speed becomes invalid. The speed is indicated as KTBT 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 ARP TARGET menu.
Canceling echo-referenced speed input
Open the SPD menu, referring to paragraph 1.13, and set 1 SHIP SPEED to
LOG, NAV or MANUAL as appropriate.
3-4
changes to
R1
R1
Reference target
in 60 seconds.