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A pH meter measures the acidity of an aqueous solution. It is the measurement of the amount of H-ions in aqueous solutions. With a pH meter, each aqueous solution can be measured to determine the pH. 

The frequency of calibrating a pH meter depends on usage and possible contamination. The higher the usage and the amount of contamination, the more often you need to calibrate your pH meter. Ensure a pH meter calibration twice a month to avoid measuring errors. It is also advisable to calibrate the pH meter in the following cases:

• When you use a new electrode.
• When the electrode hasn’t been used for a long time.
• After the electrode has been cleaned.
• After measuring a strong solution.
• When it is really important to get a very accurate measurement.

Soak an electrode newly taken from the package, or an electrode that has been dry, for a minimum of 4 hours in a cup with additive fluid. Soak a regularly used electrode in a cup with tap water for 15 minutes.

To calibrate a pH meter you will need two types of buffer solutions: pH7 and pH4. These buffer solutions help you with displaying the right pH values, because when you use a pH meter you want to be sure that the pH meter displays the right measurement. You use the buffer solutions with known pH, so you can adjust the meter. First start with the pH7 buffer solution and then the pH4 buffer solution. However, make sure to use fresh buffer solution for each pH meter calibration. You can calibrate a pH meter as follows:

• First place the electrode in the pH7 solution. After approximately 1 minute the measurement will be stable. The meter should indicate a Ph value of 7.0. If this is not the case, then establish the pH meter at this value. 
• Rinse the electrode well with demineralized water and then place the electrode in the pH4 buffer solution. 
• Repeat these steps until a reliable measurement is obtained. The pH meter will then indicate a value by measuring the pH4 solution. The further this value is from the pH4 value, the greater the discrepancy of your measuring instrument.

The terms calibrating and gauging are often used interchangeably but they are not the same. When calibrating you determine how far your pH meter deviates from the standard. You do this yourself and there are no real consequences to this: you only determine the accuracy of your measuring instrument. Gauging is official verification where a specialist determines how the pH meter meets legal regulations. There are consequences to this: when a pH meter is rejected, it may no longer be used.

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