Garmin GPSMAP 392, 398, 492, 498 Owner's Manual

Also see for GPSMAP 392, 398, 492, 498: Quick reference guide Specifications

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GPSMAP 392/398/492/498 Owner’s Manual 73U SING SONAR > SONAR PAGEWide BeamNarrow BeamThe wide beam is more helpful in shallow water, because it givesyou a much wider view of objects in the water, including areasbeyond the sides of your boat. At a 30-foot depth, the wide beamcovers the area of approximately a 20-foot circle.Understanding the Sonar DisplayOne of the first things to understand about sonar is that thetransducer sends a beam down to the bottom of the water, muchlike the beam of a flashlight. The beam starts small near your vesseland expands as it gets to the bottom.The Sonar Page does not show a 3-D representation of theunderwater environment. Instead, the display is in two dimensions,much like if you took a picture of an aquarium. Only the depth ofthe item in the water is shown.The strongest sonar returns appear on your screen as the mostintense solid color (depending on your selected color scheme; redis the default). The weakest returns appear as the less intense, lesssolid colors (blue is the default).The bottom of the water is always be the strongest signal, andtherefore the most intense color. The bottom is the continuous,intensely-colored line running across the bottom of the screen.The GPSMAP 392/398/492/498 uses the latest technology ininterpreting bottom signals; it can see through fish, structures,and thermoclines (shown in the weakest colors). However, largeschools of fish or dense structures close to the bottom can affectwater depth return readings.NOTE: If the GPSMAP 392/398/492/498 is unable to track thebottom for any reason, the digits in the depth window flash onand off to alert you that the unit is not tracking the bottom.