I have just calibrated my PH probe for freshwater, I set the first level to 4 and used calibration solution 4 and the second level to 7 and used calibration solution 7. All went well with the calibration until I tested it. I placed the probe into the Calibration solution 4 and the unit measured it as 3.0, I then placed it into the Solution 7 and it is measuring it as 5.57. I would have assumed it would have measured them as 4 and 7 respectively.
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