Claims to be calibrated Never matched test solution Tried to calibrate Every time error message I went back through the window so I have a nice little paperweight now I think a lot of these PH pens don't come out good from the factory. Just test them as soon as possible so that you can send back the defective ones. While I can't see about 1 out of 4 actually working, I've tried several other brands. This could never calibrate at all. "
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