many modern fish finders also have track back capabilities in order to check the changes in movement in order to switch position and location whilst fishing. It is easy to get more detail at screen when the frequency of fish finder is high. Deep-sea trawlers and commercial fishermen normally use low-frequency which is in between 50-200 kHz where modern fish finders have multiple frequencies to view split screen results. General interpretation The image above, at right, clearly shows the bottom structure—plants, sediments and hard bottom are discernible on sonar plots of sufficiently high power and appropriate frequency. Slightly more than halfway up from the bottom to the left of the screen centre and about a third away from the left side, this image is also displaying a fish – a light spot just to the right of a 'glare' splash from the camera's flashbulb. The X-axis of the image represents time, oldest (and behind the soundhead) to the left, most recent bottom (and current location) on the right; thus the fish is now well behind the transducer, and the vessel is now passing over a dip in the ocean floor or has just left it behind. The resulting distortion depends on both the speed of the vessel and how often the image is updated by the echo sounder. Fish arches With the Fish Symbol feature disabled, an angler can learn to distinguish between fish, vegetation, schools of baitfish or forage fish, debris, etc. Fish will usually appear on the screen as an arch. This is because the distance between the fish and the transducer changes as the boat passes over the fish (or the fish swims under the boat). When the fish enters the leading edge of the sonar beam, a display pixel is turned on. As the fish swims toward the centre of the beam, the distance to the fish decreases, turning on pixels at shallower depths. When the fish swims directly under the transducer, it is closer to the boat so the stronger signal shows a thicker line. As the fish swims away from the transducer, the distance increases, which shows as progressively deeper pixels. The image to the right shows a school of white bass aggressively feeding on a school of threadfin shad. Note the school of baitfish near the bottom. When threatened, baitfish form a tightly packed school, as the individuals seek safety in the center