Garmin gpsmap-188 User Manual

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PTIONS

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