Raymarine DSM250 Owner's Handbook Manual page 81

Chapter 5: Basic Display Controls
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BTM.LOCK
Range intervals on Bottom Lock are measured up from the bottom
(rather than down from the surface). Thus, the bottom is shown as
zero and the top number indicates the maximum distance above
the bottom being displayed. You can adjust the Bottom Lock
range.
If the A-Scope or Zoom image was displayed, selecting Bottom
Lock automatically switches OFF A-Scope and Zoom.
If you have split frequency selected, the Bottom Lock image is
displayed in both frequency windows.
If Target Depth ID is ON (see Target Depth ID on page 4-14), the
target depth is displayed as distance from the bottom.
To display the Bottom Lock image:
1. Press the BTM. LOCK soft key. The Bottom Lock selection soft
keys are displayed.
2. Press the BTM. LOCK OFF ON soft key to toggle the function ON.
3. Press the BTM. LOCK FULL SPLIT soft key to toggle between a full
window bottom lock image or split windows. The bottom lock
image is displayed.
If you select split windows, the sounder display is split vertically,
with the bottom lock image in the left hand window and the scroll-
ing bottom display in the right hand window.
In a split window display, a vertical bar appears (along the right
hand edge of the scrolling bottom image) that references the
range being displayed in the bottom lock window. This bar varies
in height as the bottom lock range is changed.
4. To adjust the range, press the appropriate BTM LOCK RANGE soft
key: press the up arrow to select a larger range, press the down
arrow to select a smaller range.
5. Press ENTER or CLEAR to return to the default display.
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