About 25 years ago I attended a weekend seminar on bass fishing...There were several different classes that we attended and one of these was on how to determine what depth you should start fishing...The instructor went through checking oxygen at different levels, checking temperature, checking ph at different levels and using a ColorSelector, of course all of these were for sale...Toward the end, I asked him if he used a depth finder, he said "Of course"...I then asked what would be wrong with cruising around with the depth finder, marking fish and then start fishing at the level that you marked most of the fish at....You could have heard a pin drop...