Furuno TS-331A - Manual (Page 21)

2. SONAR OPERATION
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2.1.3 Locked mode
This mode functions to operate the sonar as an echo sounder, with the
transducer locked at 0° sector size. The transducer location is at the top of the
sonar image display and the image data is displayed across the screen from
right to left.
Ground rope of trawl
Bottom
Individual fish
(angular echoes)
in trawl
Locked mode displa y