Furuno CH-37 - Manual (Page 25)

2-9
2.7 Detecting Fish Schools Aurally
Occasionally you will be preoccupied with other tasks and un-
able to concentrate on watching the sonar picture. In such cases
it would be a good choice to use the audio function. This func-
tion enables you to monitor echoes from fish schools and bot-
tom through the external speaker (option), of which the volume
can be adjusted with the AUDIO control on the sub panel 1.
After you become accustomed to utilizing the audio function,
you should be able to detect a fish school from a range longer
than you can detect it on the screen. In addition you may judge
whether the fish schools is approaching or going away; the
tone becomes higher when the fish is approaching and lower
when going away.