Below is procedure of manual pH calibration from Water Analytic:

1.Select Manual Calibration  

2.Place the probe in the first buffer. As opposed to auto calibration, it is okay to press Enter without waiting for the probe output to settle down. The next screen will display the current output reading of the probe. The pH is calculated from the mV reading based on the operation of a perfect probe at 25 0C, i.e. pH 7= 0 mV and the voltage increment is 59.16 mV/pH.

3.When the reading settles down press Enter. The next screen allows you to change the value of the displayed pH value to correspond to the actual pH of the calibration solution. Use the up and down arrow buttons to change the value and the left / right arrows button to change the cursor position. Press the Enter key to lock in the correct value.

4.The results of the calibration, identical to the one shown for auto calibration, will display.

5.Place the probe in the second buffer. Again, there is no need to wait for the probe reading to settle down prior to pressing Enter.

6.When the reading settles down press Enter. Change the pH reading to the pH of the calibration standard.

7.In the final step of the pH calibration process, the screen will display parameters of the calibration process such as: Slope, Efficiency, Offset. If Efficiency is below 80%, the pH probe is damaged, recommend should replace it with another pH probe

User can refer the function of pH transmiter AM 2250TX at here