What Is The History of Fish Finders?

Brief Explanation and History of Fish finders:
Fish finders are basically a type of SONAR (sound navigation and ranging). Fish finders use "active" (rather than passive which does not produce the sound) sonar to detect fish. Fish finders also detect the bottom of the ocean or lake, and everything else that reflects the sound beam.

The transducer (usually included with the fish finder) produces the sound beam which reflects off anything under the boat. These reflections are interpreted and displayed on the graphic display (usually a LCD or CRT screen) of the fish finder.

Fish finders get their origins from fathometers. Modern fathometers (meaning fathom plus meter) are designed specifically to show depth and usually only have a digital display. Early fathometers were comprised of a flashing rotating light at the edge of a circle.