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Glossary Sonar Terms
Alarm, Depth: Depth Alarm is a user-controllable, audible alert that sounds when depth is less than or equal to the setting.
Alarm, Temperature: Temperature Alarm is a user-controllable, audible alert that sounds when the water surface
temperature equals the setting.
Backlight: Backlight is a user-controllable illumination for the LCD for night and low light use.
Beam (Sonar Beam): A sonar beam is the wide, cone-shaped projection of sound waves formed as sound travels
underwater. See Cone Angle.
Big Digits View: Big Digits View is a Humminbird® feature that displays the sonar graph and enlarged digital readouts for
easy reading from a distance. This is a great tool when monitoring the digital depth is important - such as with higher boat
speeds, or when viewing the unit from a distance. When speed input is available, the Big Digits View also shows the TripLog.
See TripLog.
Bottom Black: Bottom Black is a Humminbird® feature that "fills in" the area of the display below the bottom contour.
Bottom Black is preferred by some anglers because of its high contrast and easy readability, even though it can obscure
bottom hardness information.
Bottom Contour: Bottom Contour is the profile of the bottom graphed to the display as the depth changes.
Bottom Hardness: Bottom Hardness is the density (or composition) of the bottom, which can often be determined by
interpreting the main sonar return. Varying levels of hardness can be determined by interpreting the "thickness" of the sonar
return. Hard returns appear thin and black, softer returns appear thicker and less black. It is important to note that a sonar
return from a sloping bottom can have the appearance of a softer bottom.
Cavitation: Cavitation is the effect of air bubbles created as the propeller rotates and the boat moves through the water.
Chart Speed: Chart Speed is a user-controllable feature that sets the speed at which sonar information moves across the
display. A faster setting displays sonar information from more pings and shows more detail, but the information moves
quickly across the display: a slower setting permits viewing of more sonar history, but does not display as much detail. The
best setting is often the user's personal choice.
Cone Angle: The cone angle is the angular measurement of the sonar beam at a specific dB down point (i.e. -10 dB). See
dB Down Point.
Customizable Digital Readouts: Customizable Digital Readouts is a Humminbird® feature that permits the user to select the
specific digital information that appears in the main Sonar view (i.e. Speed, Temperature, Barometric Pressure, TripLog, etc.)
Dead Zone: The dead zone is the area of the sonar beam that receives the sonar signal after the main bottom return. Fish
and other objects close to the bottom that fall within the dead zone will probably not be visible in the sonar beam. Precision
sonar beams, such as the Humminbird® 20° beam, have a smaller dead zone than wider sonar beams.
Decibel: A Decibel is the measurement for sound pressure level, or "intensity" of the sonar return. See dB Down Point.
dB Down Point: The dB Down Point is the standard decibel level at which the sonar cone angle is measured, and is
written as "@ -10 dB" or "@ -3 dB". Measurements at smaller down points (bigger negative numbers) indicate that the
less intensive sonar signals are being used for the measurement.
Display, FSTN: FSTN is an acronym for Film Super-Twist Nematic. FSTN is a monochrome display technology
characterized by black, high-contrast pixels. All monochrome fixed mount Humminbird® products use FSTN technology.
DualBeam PLUS™: DualBeam PLUS™ is a Humminbird® sonar configuration that uses two sonar beams
simultaneously, and combines the information from both beams into one view by overlapping the data on-screen, or
shows each beam individually side by side, or permits each beam to be viewed individually full screen.
Feature Memory: Feature Memory is a Humminbird® feature that retains the user's menu settings in permanent
memory. Settings are retained even when the unit is powered off indefinitely.