The swing of the pointer of the acidity meter indicates that the measured data is unstable, and these aspects should be considered: voltage problem. If the voltage is unstable, the instrument measurement will be unstable. If the previous measurement is normal, this is generally not a problem. At this time, you can use the following methods to check whether the machine is normal, remove the electrode and short-circuit the electrode interface of the fuselage. At this time, the mv value of the instrument is 0, which remains stable. Then switch to the pH position and adjust the positioning knob. At this time, the pointer can be displayed. I think it should be your machine for a long time. The knobs and switches may be dirty. Take some anhydrous ethanol, add it to the knob and switch, twist it a little more, and then turn it on. Next, connect the electrodes, put them into 6.86 buffer, and check the current mv value. It will stabilize in half a minute. If it keeps jumping, it means that the electrode connection or instrument connection is not good. If the interface is too dirty, clean it. When it is relatively stable, take a look at its mv value, which should be within 20mv from 0, indicating that your standard scheme is OK, otherwise it needs to be reconfigured. There is nothing wrong with the calibration. If it jumps during the measurement, if you are measuring distilled water or pure water, it is recommended that you use a reference electrode and a separate electrode for measurement. At this time, the composite electrode is not very good because the input impedance of the liquid and the instrument does not match.