Furuno FAR-2218 Operator's Manual page 146

3. TARGET TRACKING (TT)
4. Repeat step 3 until to place up to three reference points.
5. Right-click to deactivate the reference mark
function.
6. Right-click the [SPD] indication at the top-right of
the screen to show the [SPEED] menu.
7. Select [2 SHIP SPEED].
8. Select [REF].
9. Close the menu.
It takes approximately one minute for the speed
to appear in the own ship information box. When
the speed appears, the indication "REF BT" also
appears to the right of the speed value.
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 mov-
ing target produces error in the vector for TT and AIS, which results in wrong colli-
sion avoidance information. Further, an unstable stationary target produces
inaccurate speed data and the target itself may become lost.
• On IMO-type radars with AIS in use, echo-referenced speed is shown in gray to in-
dicate they are not available for selection.
• 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 alert box.
If all reference targets are lost, the speed indication reads "*.*" Select a different ref-
erence target if currently selected one is lost.
• When all targets are deleted, the reference target mark is also deleted and the tar-
get-based speed becomes invalid. The speed is indicated as "BTREF" where BT
means Bottom Track (speed over ground).
• Reference targets can be marked with a vector.
This can be done with [4 DISP REF TGT VECTOR] on the [TT] menu.
• Loss of reference target will affect the calculation of true speed and true course of
targets. Further, own ship speed will be inaccurate.
How to cancel echo-referenced speed input
1. Open the menu.
2. Select [7 INFORMATION BOX].
3. Select [2 OWN SHIP INFO].
4. Select [3 SPEED]. The [SPEED] menu appears.
5. Select any option, other than [REF], then press the ENTER MARK key.
6. Close the menu.
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