Raymarine GPM400 Reference Manual page 97

Adjusting the position of the zoomed area
When the zoom function is selected, the system automatically
selects the zoom position so that the bottom details are always in
the lower half of the display. If required you can reposition the por-
tion of the image to be zoomed so that an alternative area is
displayed.
To set the zoom position
1. Press the ZOOM softkey.
2. Select MAN with the ZOOM POSITION softkey.
3. Reposition the zoomed image using the rotary controller.
4. Press OK.
Bottom lock and bottom shift
The Bottom Lock function applies a filter to flatten the image of the
seabed and make any objects on or just above it easier to discern.
This feature is particularly useful for finding fish that feed close to
the bottom.
Bottom Lock is selected for individual fishfinder windows and can
replace or appear alongside the standard fishfinder image.
Adjusting the range of the bottom lock image allows you to view
more bottom details. You can also reposition the image on screen
to anywhere between the bottom of the window (0%) and the mid-
dle of the window (50%) by using the Bottom Shift control.
Bottom lock range
(distance from bottom)
SHALLOW Freq1: 200 kHz-Auto
F1: 200 kHz
BL
Depth
reading
Bottom
shift
ADJUST SELECT OPTION
FREQ1 FREQ2 BOTTOM LOCK
Bottom lock image
D10412-1
To adjust bottom lock
1. Toggle to FULL or SPLIT.
2. Use the appropriate softkeys and rotary controller to set the
range and bottom-shift values.
Using A-Scope to view a live image
The standard fishfinder display shows a historical record of fish-
finder echoes. If required, you can display a live image of the
bottom structure and the fish directly below the transducer by using
the A-Scope feature. The width of the bottom area covered by the
A-Scope is indicated by the number at the bottom of the window.
The A-SCOPE softkey
When A-Scope is on you can select one of three display modes:
97
Depth from the surface
Freq2: None
BOTTOM LOCK B-LOCK RANGE BOTTOM SHIFT
FULL SPLIT 50ft 14%
Standard fishfinder image
Chapter 8: The Fishfinder