DD - since you said that your screen is scrolling from right to left I assume you are viewing either traditional 2D sonar or down imaging sonar. The question you pose illustrates the problem with both 2d and DI. Truth is you don't and can't know from either 2D or DI to which side the object is or if the object is directly below you. Only SI can give you that info and is why, in my opinion, SI is generally more useful. And DI has limited usefulness.