Furuno CSH-8L - Manual (Page 55)

4. ECHOSOUNDER
4-5
4.7 Erasing Weak Echoes
Sediments in the water or reflections from plankton may be painted on the
screen in green or light-blue, as shown in the illustration below. These echoes
may be erased in order of strength as below.
Weak reflections
Weak echoes
1. Press the [MENU] key to open the menu.
2. Use the [RANGE] control to choose [MENU MODE] at the top of the screen.
3. Use the [GAIN] control to choose SOUNDER.
4. Use the [RANGE] control to choose DELETE COLOR.
5. Use the [GAIN] control to choose setting desired. The setting range is 0-10,
and the higher the setting the stronger the echo that will be erased.
6. Press the [MENU] key to close the menu.