Calibration work is completed, the use of frequent pH meter generally within 48 hours the instrument does not need to be re-calibration. If you encounter any of the following conditions, the instrument needs to be recalibrated:
⑴ solution temperature and calibration temperature have a greater difference.
⑵ electrode exposed in the air for too long, such as more than half an hour.
⑶ positioning or slope regulator is malfunctioning;
⑷ measured acid (pH <2) or over-alkali (pH> 12) solution;
⑸ replaced after the electrode;
⑹ When the pH value of the solution under test is not in the middle of the selected solution at the two point calibration, and further away from 7pH.