okay i am very new to this and don't even have SI unit...not yet at least...so let me see if can get how this works:

just for the sake of this being pretty simple lets use the picture that has the "fish next to the bamboo". now those fish are off the left side of the boat and about 30ft away? the unit says "40 left" so i am thinking from the boat to the end of the picture would be 40 ft. judging by where the fish are they are probably from 25-35 feet away? also judging by the shadow they would be close to the bottom?

let me know if i'm close.