Your sonar is showing the distance from the transducer to the mark. So if that fish is off to the side 100' from the transducer, it could only be 80 or 85' down. If it is directly below the transducer, it could truly be at 100'. Imagine your boat at the top of a piece of paper. Now draw a smiley face below it. Anywhere on that smiley face will be the same distance from the boat. The further off to the side of the smile, the shallower the fish is. Make sense? Sent from my SM-A505U using Tapatalk