Greatly simplified, this fish finder is just a combination of a speaker, microphone and stopwatch. It transmits a sound pulse from the sonar sensor, and then measures the time it takes for the “echoes” to return to the sonar sensor (The fish finder "knows" that the speed of sound through water is about 4800 feet per second).
Fish, rocks, logs, weed, debris, the bottom, etc all “echo” the pulse at a different intensity. A built-in computer then organizes all of this information and shows it on a display screen in a manner that is easy for the user to understand.
The depth readout on the upper left corner will appear after the power is turned ON and the sonar sensor is placed in water between 2 feet and 240 feet (.5 to 75 meters). If the depth exceeds these parameters, the depth meter will indicate “---”. This reading may also occur in water that is extremely dirty, or where there are heavy silt or mud bottoms. Sonar is a sound signal that travels through water. Sonar will not travel through air. Keep this in mind when using the fish finder, as the smallest air bubble between the sonar sensor and the water will cause the Fish Finder to not operate correctly.
If the fish finder determines that sonar has detected a fish, the display will show a fish shaped icon. The first column of fish indicators on the right of the display shows the most current information. This column is then moved to the left as a new reading is displayed. That is, fish indicators “swim” away from the right to the left at a constant speed. This motion in no way reflects actual movement of the fish.
Fish Depth Indicator
Use the Fish Depth Indicator to measure the fish’s depth from the Sonar Sensor. This can be done by dividing the depth reading by 10. This number represents the value of each box.
(Example: The depth is 29.3 feet, the fish symbol appears in the 4th box from the top. This means the fish is 7 to 8 feet from the surface)