Calibration of your meter is an important consideration if you are going to rely on your meter for your results and to ensure that the readings it provides are accurate. There are no hard and fast guidelines for calibration frequency, it depends on the meters individual specifications, parameter being measured and the product being measured and whether it has any impact on the meter or sensor performance.
Calibration Frequency
As mentioned above, there are no hard and fast rules about frequency of calibration. For products such as thermometers and humidity meters, an annual calibration check is considered best practice. This is because in general use these type of meters don't 'drift' and the sensor technology is pretty robust.
For Conductivity, Dissolved Oxygen and pH it is a different matter. Of the three, Conductivity sensors are the least sensitive to drift and many operators only check the calibration once a month or so using a solution with a known conductivity value suitable for the range of their meter. Dissolved Oxygen sensors and pH sensors can be greatly affected by the medium they are measuring within and may require calibration or calibration checking as often as once a day, to as infrequently as once a month.
