of the school. This typically looks like an irregularly shaped ball or thumbprint on the fishfinder screen. When no predators are nearby, a school of baitfish frequently appears as a thin horizontal line across the screen, at the depth where the temperature and oxygen levels are optimal. The nearly-vertical lines near the right edge of the screen show the path of fishing lures falling to the bottom. General history in sporting and fishing The first fishfinder that was marketed for consumers in America that was meant for recreational fishing was the Lowrance Fish Lo-K-Tor (also nicknamed "The Little Green Box") which was invented in 1957 and entered market in 1959. It was not the first fishfinder, ie. sonar device meant to find underwater fish or schools of fish, as in 1948 in Japan the Furuno brothers introduced a fishfinder for use in commercial fishing vessels; this Furuno Fish Finder is said to be the world's first practical fishfinder. The Fish Lo-K-Tor's operation was as described below (neon lamp readout device etc.). By the early 1970s, a common pattern of depth finder used an ultrasonic transducer immersed in water, and an electromechanical readout device. A neon lamp mounted on the end of an arm was rotated around a circular scale at a fixed speed by a small electric motor. The circular scale was calibrated in terms of depth of water. The instrument was arranged to send out a pulse of ultrasonic waves as the lamp passed the zero point of the scale. The transducer was then arranged to detect any reflected ultrasound impulses; the lamp would flash when an echo returned to the transducer, and by its position on the scale would indicate the elapsed time and therefore the depth of the water. These also gave a small flickering flash for echos off of fish. Like today's low-end digital fathometers, they kept no record of the depth over time and provided no information about bottom structure. They had poor accuracy, especially in rough water, and were hard to read in bright light. Despite the limitations, they were still usable for rough estimates of depth, such as for verifying that the boat had not drifted into an unsafe area. Eventually, CRTs were married with a fathometer for commercial fishing and the fishfinder was born. With the advent of large LCD arrays, the high power requirements of a CRT gave way to the