Furuno FR-1710 - Manual (Page 28)

1-14
1.18 Measuring the Range
Measuring range by the fixed range
rings
Use the fixed range rings to obtain a rough
estimate of the range to a target. They are
concentric solid circles about own ship, or the
sweep origin. The number of rings is auto-
matically determined by the selected range
scale and their interval is displayed at the
upper-left position of the screen. The fixed
range rings may be turned on/off and their
brilliance adjusted with the [RINGS] key.
Measuring range by the variable
range marker (VRM)
Use the Variable Range Markers (VRMs) for
more accurate measurement of the range to
a target. There are two VRMs, No.1 and No.2,
which appear as dashed rings so that you
can discriminate them from the fixed range
rings. The two VRMs can be distinguished
from each other by different lengths of
dashes.
1. Press the [VRM ON] key to display either
of the VRMs. Successive presses of the
[VRM ON] key toggle the active VRM
between No.1 and No.2 and the currently
active VRM readout is circumscribed.
2. Rotate the VRM rotary control clockwise
or counterclockwise to align the active
VRM with the inner edge of the target of
interest and read its distance (unit: nm)
at the lower-right corner of the screen.
Each VRM remains at the same geo-
graphical distance when you operate the
[RANGE] key. This means that the appar-
ent radius of the VRM ring changes in
proportion to the selected range scale.
3. Press the [VRM OFF] key to erase each
VRM.
0.55 NM
15.0
°
R
Ring interval
No. 1 VRM
(dotted)
VRM
0.375NM
0.550NM
Cursor
Target
No. 2 VRM
(dashed)
Range to
No. 1 VRM
Active marker is
circumscribed.
Range and
bearing to
cursor
Range to
No. 2 VRM
Figure 1-15 How to measure
range by VRM
1.19 Measuring Bearing
Use the Electronic Bearing Lines (EBLs) to
find bearing of a target. There are two EBLs,
No.1 and No.2, which are toggled by suc-
cessive presses of the [EBL ON] key. Each
EBL is a straight dashed line extending out
from the own ship position up to the circum-
ference of the radar picture. The fine dashed
line is the No.1 EBL and the coarse dashed
one is the No.2 EBL.
1. Press the [EBL ON] key to display either
of the EBLs. Successive presses of the
[EBL ON] key toggle the active EBL be-
tween No.1, No.2 and index lines (if dis-
played) and the currently active EBL
readout is circumscribed.
2. Rotate the EBL rotary control clockwise
or counterclockwise until the active EBL
bisects the target of interest, and read its
bearing at the lower-left corner of the
screen.
3. Press the [EBL OFF] key to erase each
EBL.
The EBL readout is affixed by “R” (relative) if
it is relative to own ship’s heading, or “T” (true)
if it is referenced to the North, as determined
by the item EBL/VRM on the OTHER menu.