Furuno SFD-1010 Operator's Manual page 131

Zero line rejector
When turned on, the zero line rejector
functions to distinguish fish echoes near the
surface. The tail length of the zero line
changes with transducer type and installation
state. When using a transducer with a zero
line of 1.4 m or more, change the setting for
[Zero Line Rejector], as shown below.
Zero line rejection area
This menu appears only when DFF3 is used. If
the zero line tail is long, increase the value. If
this does not delete the zero line, lower the
transmission output value.
Bottom detection level (LF), bottom detection level (HF)
In the factory default setting (0), the equipment judges consecutive strong echoes to be
bottom echoes. If the depth indication is unstable, adjust the bottom detection level. If
lines extend upward from the bottom line in the bottom lock display, lower the bottom
detection level to erase these lines.
Bottom lock display
Bottom
3. FISH FINDER
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