Eagle FISHMARK 640C, Installation And Operation Instructions Manual

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harder (more rocky) the bottom, the easier it will be to get a second bot-
tom signal. Don't touch the controls once they've been set.
Example of a second bottom signal. Unit is in 30 feet of water, with
range set at 80 feet and sensitivity set at 87 percent
2. Next, take the transducer out of the water and place it in the water
in the sump of the boat, face down. (The transducer face is shown in the
figure on page 25.) Notice how the signal strength decreases. The sec-
ond bottom signal will probably disappear and the bottom signal inten-
sity will likely decrease.
3. Now move the transducer around to find the best location with the
strongest possible bottom signal. If you find a spot with an acceptable
bottom signal, mark the location and move on to step 4.
If you can't get an acceptable bottom signal, try turning up the sensitivity
by three or five keystrokes and then move the transducer around once
more. If you find a spot that works, mark it and move on to step 4.
If you have to turn up sensitivity by more than five keystrokes to get a
good signal, the transducer should be mounted on the outside of the
hull. This is especially true if you have to turn sensitivity all the way
up to get a decent bottom signal.
Second bottom
True bottom
Manual range setting