I have had a problem with my Humminbird reading the correct depth. I lost my head unit a while back, so I ending up buying a whole new unit. I had this problem before with my old unit. I replaced the transducer, and head unit, used the same base and power wire that I had already installed. While on the lake for a couple hours, everything works fine. And all of a sudden, the unit will start reading 0.9'. It will still show bottom contour, and read a accurate water temp, but will not show the depth right. I have checked the angle of the transducer and everything looks fine. What could be my problem??????????