I've had my ACJr. for a little over a year. It's been working fine, but lately, I noticed that it's not reading the proper temperature. As a reference, I put a floating mercury in the tank and the two are off by several degrees. I then adjust the temp. calibration of the ACJr. so it matches the merc. therm. It's fine for a about a day and then the two are off again. I called Neptune Systems and they are no help at all. I ordered a new probe in the PA Group Buy, but was wondering if anyone else had this problem.