Bottom Lock Soft Key; Fig. 3-12 Bottom Lock Display - Raymarine L750 Operating Handbook

Chapter 3: Operating Instructions

Bottom Lock Soft Key

The normal display on the Fishfinder is a "top-down" view, as if it was seen
from the surface of the water. When the Bottom Lock feature is turned on,
the unit shows a "bottom-up" view. The bottom is used as the reference,
and echoes from objects directly above the bottom are displayed. See Fig.
3-12. This feature is helpful when searching for types of fish which feed
close to the bottom.
Part of
down-
looker
page
Bottom
lock
image

Fig. 3-12 Bottom Lock Display

Here are the special items on this display:
Bottom Lock Image
Figure 3-12 shows a display which has been modified using the
Bottom Lock feature. The right side of the display shows part of the
familiar Downlook image. The left side shows the Bottom Lock
image. The bottom is indicated as a straight line. The actual
bottom is not flat like this, of course. The straight line represents the
part of the bottom which is actually under the boat at the moment.
The depth of the bottom represented by the line will change from
moment to moment, as the shape of the bottom changes. The
Bottom Depth reading shows the current depth represented by the
line. Notice that some of the bottom features may extend above
this line.
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Top of
bottom
lock
range
Bottom
lock
area