Humminbird Wide View Operation Manual page 32

Once you are in zoom, refer to the preview area and adjust the depth of the zoom range
by using the UP and DOWN arrow buttons. The Zoom menu will not appear when an adjustment
is made unless MENU is pressed.
The digital depth readout will continue to track the bottom even when Zoom is enabled.
Bottom Lock is a function of zoom, except the depth adjustment is controlled
automatically to view the area immediately above the bottom. This is especially useful if you are
looking for structure or minor variations in terrain in areas of relatively flat bottom terrain. To
enable Bottom Lock, press ENTER until the "BL" is highlighted. The zoom range will be controlled
by the current depth range, as in Zoom, and will be indicated on the Zoom menu.