Furuno GP-7000F Operator's Manual page 92

10. VIDEO SOUNDER OPERATION
Bottom-lock display
The bottom-lock display provides a compressed normal picture on the right half
of the screen and a 15 or 30 feet (5 or 10 meter) wide layer in contact with the
bottom is expanded onto the left half of the screen. This mode is useful for
discriminating bottom fish from the bottom echo.
Note: The range of the bottom-lock display can be changed at BOTTOM LOCK
RANGE on RANGES menu.
Bottom-zoom display
The bottom-zoom display expands bottom and bottom fish echoes by the chosen
zoom range and is useful for determining bottom hardness. A bottom displayed
with a short echo tail usually means it is a soft, sandy bottom. A long echo tail
means a hard bottom.
Note: The range of the bottom-zoom can be changed at ZOOM RANGE on
RANGES menu.
10-6
88.7
Bottom-lock display plus normal sounder display
59.8
ft
Bottom-zoom display plus normal sounder display