Well with todays electronics, it truly doesn't make that much of a difference...I always figgured if the engineer that designed the circuitry and sofware could figgure out which return signal met enough criteria to warrant a fishy symbol over those that dont was good enough for me  :grin: I've tried and tried with the arches to figgure out which were clutter and which were real and so forth,,but just gave up on it.  But like I said with today electronics vs 15 or 20 years ago, it really dont matter.  Most of your better Humminbird Units now show both the fishy's and arches, so why not display em both.

Well I was on the theory that the longer the arch the bigger the fish----well sort of that works,,,but its more of a time element as the fish enters and exits the sonar cone---so a little bitty fish that swims slowly thru the cone could show up a lot bigger than what  you invision him to be and vice versa if a great big fish zips thru it would decrease the time in the cone and show up as a shorter arch.

I was also told once that the bigger the hump of the arch that it meant a bigger fish,,,well that one dont hold water either because if the fish entered the cone then traveled directly thru the center it would leave a higher arch than one that skirted along the side of the cone.....this is because the distance (depth) is shorter when directly underneath the transducer vs when it enters the cone.

So what is the sonar actually doing---it simply bounces off of an object and based on the density of that object, so now we can throw out the air bladder theory that you may or may not have heard of.  Sonar doesnt bounce off of air,,it just kinda absorbs the sound energy and since all depictions on your sonar screen are assimilated sonar returns,,,there just wont be anything there to represent. :?  With one exception,,and that is the Side Imaging technology of Humminbird units....Those air bladders now show up as "White Holes" in the image.

So how in the heck do you figgure out which arches are little fish and which ones are bigger fish....Well based on time, distance, signal strength of the echos, it can only come with a lot of time using the unit and faith in the unit.  Otherwise I'll just go with the Engineers opinon that X number of returns, over time Y, multiplied by Z signal strength warrants a small fishy symbol, a medium fishy symbol, or a large fishy symbol at the depth constant of D/pi and use my slide rule for a cutting board  :P