The sonar s side-finder shines when locating springs during warm weather. Since sand is usually built along with the spring discharge I m always suspicious of lake-bottom humps that don t reflect a rock signal. The vertical sonar function can be used to delineate these and locate them after a thermometer verifies a seep or discharge. For the more affluent, a dissolved oxygen meter can verify if it s a good spring or one that finds its genesis so deeply that it is anaerobic. Although I have never been able to consistently do it with my Fishing Buddy, a sonar can also delineate the thermocline so one can adjust their technique to select the lakeside structures that coincide with the level just above.
More powerful units can.
The fishing buddy will sometimes show a line of fish suspended over deeper water. It quite often speaks with forked tongue. That is the thermocline but don t stake your entire trip s success on it. Just as it will mark a fish that you can see clearly is not there, or the side finder will mark a fish when your patrolling a shoreline only the fish is some thirty feet up the bank, you re dealing with a less than perfect instrument. Nonetheless long experience will tell you that on days when there are few hooks on the side finder, probably there are few fish in a feeding mode and when you start to see an abundance and get no strikes, it s time to change flies.