you say you havent marked a fish, but dont know where your balls are? if you arnet reading your balls on your graph, i wouldent worry about seeing fish on it........ because you got other problems
temp at the ball is more important than "seeing" fish on your graph anyways
and assuming your graph isnt junk, how is the angle of your transducer..... does it seem to work right in shallow water? skip out at more than a troll??? if your catching fish, are you duplicating any constant???
i need some more information to assess this situation.
but my gut tells me your running some old ass graph