Furuno NAVNET GD-1920C Operator's Manual page 124

HF picture
The higher the frequency of the ultrasonic pulse the better the resolution. Therefore, the
high frequency is ideal for detailed observation of fish school.
Marker-zoom display
The marker-zoom display expands a selected area of the normal sounder picture to full
vertical size of the screen on the left-half window. You may specify the portion to expand by
operating the VRM (Variable Range Marker), which you can shift with the ENTER knob.
The area between the VRM and zoom marker is expanded. The length of the segment is
equal to one division of the depth scale.
Note: The VRM is set independently from other displays in case of multiple displays.
Sounding area and transmission frequency
Fish school
-
-
Fish
-
school
50
-
-
-
-
-
-
60
-
-
-
-
-
-
80
70
-
HF
MARKER-ZOOM
DISPLAY
Marker-zoom display plus normal sounder display
4. VIDEO SOUNDER OPERATION
low frequency
high frequency
0'20"
0
-
-
-
VRM
-
42.0
This part
50
-
is zoomed.
-
-
Zoom marker
-
100
-
-
NORMAL
DISPLAY
4-3