Garmin GPSMAP 188C Sounder User Manual download pdf (Page 93)

GPSMAP 188/188C Sounder Owner’s Manual 87

USING SONAR > SONAR TAB OPTIONS

Keel Offset—used to offset the surface reading for the depth of

a keel. This makes it possible to measure depth from the bottom

of your keel instead of from the transducer’s location. Enter a

positive number to offset for a keel, or enter a negative number to

compensate for a large vessel that can draw several feet of water.

The Keel Offset reﬂects in the depth reading.

Keel Offset:

Transducer at

Surface Enter (+)

positive number to

show depth from

bottom of keel

Keel Offset: Transducer

at Bottom of Keel Enter

(-) negative number to

show depth from surface

Map Split Sonar Detail—controls Map Page sonar split range

scale. Full Range shows the entire scale of 2X or 4X left side split

of Sonar Page. Maximum Detail displays what is shown on the left

side of a split sonar screen.

Background Color—sets the background color on the Sonar Page

to Black, Blue, or White.

Calibrate Water Speed—this is only available if you are using

a speed-capable transducer/sensor. Calibration is required to

ensure the Water Speed displayed on your unit is accurate. The

unit automatically use the GPS ground speed, if it is available,

for comparison on the calibration. If a GPS ground speed is not

available, use either your boat’s speedometer reading (not always

accurate) or a stopwatch to determine your speed over a certain

distance (distance / time = speed). It is recommended that the

calibration take place in water having little or no current.

Calibrating the

Speed Sensor

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Garmin GPSMAP 188C Sounder User Manual Page 93