Humminbird 515 - Manual (Page 73)

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QuadraBeam PLUS™: QuadraBeam PLUS™ is a Humminbird® sonar
configuration that uses four sonar beams for a more detailed bottom image.
QuadraBeam™ uses the DualBeam PLUS™ configuration for downlooking,
and also adds two additional beams to look to the left and right. The sonar
beams pointing to the left and right provide the ability to spot fish and
structure over a wide 90° area, and to identify on which side of the boat they
are located. See DualBeam PLUS™.
Quick Disconnect Mount: The Quick Disconnect Mounting system is an
exclusive Humminbird® feature that permits the unit to be easily removed from
the mounting base by pressing a release button, and re-installed by simply
snapping it back into place. All cable connections are made when installing, so
that no separate wiring connections are required. Additionally, the mount offers
90° tilt and 360° swivel capability to adjust the viewing angle of the unit as you
move about the boat.
Real Time Sonar: Real Time Sonar is a Humminbird® technology that delivers
ultra-fast sonar transmitter/receiver operation and results in a more detailed
instantaneous view of what is under the boat. The Real Time Sonar window
is a vertical band at the right side of the display that shows the instantaneous
sonar return from the transducer at a particular instant. The RTS® Window
menu option permits the user to adjust the window to show the full sonar
signal return, or just a narrower band that indicates intensity using grayscale.
Real Time Sonar relies on very fast Sonar Update Rate (Ping Speed). See
Sonar Update Rate.
Receiver: See Transmitter.
Second Return: The Second Return is a term that describes the appearance of
a second sonar return below the primary sonar return (bottom contour) at
exactly twice the true depth. The second return is caused by the same sonar
energy bouncing off the bottom once, rebounding to the water surface and
then traveling back down to the bottom to be reflected again. Second returns
are more common in shallow water and over hard bottoms; it is actually
possible to see a third sonar return under some circumstances. The second
return provides useful information to help determine bottom hardness, as areas
with harder bottoms will generally create a second return. The second return
can be used as a guide to set Sensitivity when in shallower water.