Today,all fishfinders operate using Sonar. Sonar,developed during World War II, this technology uses sound waves to "view" underwater objects. A sound wave is produced by the fishfinder and sent through the water. At the source, the wave is narrow; however as it penetrates deeper, the sound wave spreads forming a cone, or what is commonly called a beam (think flashlight). When the sound wave encounters something within this beam, it bounces back to the fishfinder. By measuring the very small amount of time between when the sound wave was send out and when it bounces back your fishfinder calculates the distance and draws it on the screen.

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