Let me explain a little further on how I knew it was bad. When you calibrate, you poor the 4.0 and 7.0 calibration liquids into separate containers, just enough for the meter probe to immerse. The meter has an electronic calibration system in that first it calls for 7.0 juice, you put it in, wait, then it calls for 4.0 juice, you transfer it over, wait, and then it's done. My meter began displaying "error" when inserted into the 4.0. I tried new solutions, cleaning, soaking, but nothing worked. And, my readings would drift upward. The longer I let it sit, the higher it would drift, I don't know if it was drifting "toward" or "away" from a true reading, but it was unusable.