White Line; Speed Cal; Temp Cal - Raymarine L750 Operating Handbook

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When the fish symbol is turned off, the unit indicates a fish by
showing an arch-shaped line. See Fig. 3-4. This kind of display
does not include the depth readings for the fish.

White line

This feature controls the way the unit indicates the upper surface of
the bottom structure. When the feature is turned on, the unit
displays a dark line along the upper edge of the bottom image. This
makes it easier to locate any fish which are very near the bottom.
Sidelook
This item is used with the optional "Sidelooker" transducer. This
type of transducer sends sound waves out to the sides of the boat.
See Fig. 3-21. If you have installed a Sidelooker transducer, use
this line of the display to turn on the Sidelooker feature.

Speed Cal

This unit can detect and display the speed of the boat through the
water. It also uses the speed information to calculate the distance
traveled (the "log"). The item for Speed Cal allows you to adjust the
speed reading to make it match your actual speed through the
water. It presents a reading in percentage points. A reading of
100% means the speed readings from the factory default
calibration are accurate, and the unit does not need any correction.
If the unit says that you are moving faster than you really are, you
can adjust the Speed Cal figure to a smaller number. If the unit
says that you are moving slower than your actual speed, use a
larger number for Speed Cal. The setting can range between 75
and 125. Use the left- and right-controls to change the value. For
more information, see the section on "Calibrating the Sensors."

Temp Cal

This unit can display the water temperature. You may want to fine-
tune the signal from the transducer to get an accurate display. The
displayed number indicates an offset added to the measured
temperature. (This offset will be measured in °F or °C, depending
on the setting used for Temp Units.) For example, if the
temperature reading on the display tends to read 2°F too high, you
can correct for this by setting Temp Cal to -2.0°. The setting can
range between -9.9° and +9.9°. Use the left- and right-controls to
change the value.
L750 Fishfinder: Installation and Operation Handbook