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82 GPSMAP 188/188C Sounder Owner’s Manual
USING SONAR > SONAR PAGE
Whiteline—controls how the unit displays
information about the bottom type (hard or soft).
With the Whiteline Off, the bottom return displays
as red and contains no information on bottom
hardness. With Whiteline set at Normal or 1-100%,
the bottom return becomes white with a red line
indicating where the water meets the bottom. To
turn the Whiteline Off, press the ROCKER down
until the setting bar is all the way at the bottom
of the range and reads Off. See page 91 for more
detail on this feature.
Frequency—allows you to choose a transducer
frequency. Frequency refers to the pitch of the
sound that the transducer sends and receives. You
can choose 200kHz, 50kHz, or Dual frequency.
Depth Line—adds a horizontal depth line across
the display that is used to measure the depth of
underwater objects. The depth of the line appears
in a box on the right side of the line. Press up or
down on the ROCKER to control the position of
the line on the graph. The depth is displayed in a
window on the right side of the line. To turn the
Depth Line Off, press the ROCKER up until the
setting bar is all the way at the top of the range
and reads Off.
Noise Reject—helps filter unwanted noise from
the graph. The Noise Reject tool can be turned Off,
set to Normal (automatically adjusts for optimum
viewing), or to a fixed 1-100% setting. When
setting the Noise Reject tool, the HIGHER the
noise rejection setting, the less likely the unit is
to NOT show fish or structures. To turn the Noise
Reject Off, press the ROCKER down until the
setting bar is all the way at the bottom of the range
and reads Off.
Whiteline
Adjustment
Frequency
Adjustment
Depth Line
Adjustment
Noise Reject
Adjustment