Raymarine stand-alone master instrument - Manual (Page 32)

Chapter 6: Calibration 29
Offset
The instrument measures the water depth below the transducer. To
display water depth below the keel or to the surface an offset must be set
up. A negative offset is used to reduce the displayed value to give water
depth below the keel. A positive offset will give water depth to the surface.
Waterline
Waterline
Offset
Actual
Water
Depth
Depth Below Transducer
Actual
Water
Depth
Depth Below Transducer
Waterline
Depth
Below
Keel
D692
Keel
Offset