Furuno FSV-30 Operator's Manual page 114

4. ECHO SOUNDER MODE
Fish histogram
The fish histogram shows, in graph form, signal strength distribution for the fish
school(s) marked with an estimate mark on the horizontal and echo sounder
displays. The histogram display for each of those displays will be different since
the calculation method is different. This data appears only when an estimate
mark is active. When two estimate marks are active histograms are displayed
one on top of the other as below.
The horizontal axis shows signal strength in 16 colors, and the vertical axis
shows fish school concentration inside the fish estimate mark. For the fish
estimate mark inscribed on the horizontal display the graph shows the average
movement in five scans, to increase accuracy.
Note: The histogram display is redrawn five transmissions after a fish estimate
mark is erased and another mark of the same number is entered soon
after.
Estimate mark 1 or estimate
mark 2 displayed
4-14
Fish estimate
mark source
2 SCAN1
Fish estimate
mark no.
1 ES2
2 SCAN1
Blank when no estimate mark
is inscribed on the horizontal
display
Both estimate marks displayed
Fish histogram
SCAN1 for H1 display
SCAN2 for H2 display