After weighing and temperature measurement, pH is among the three most frequent measurements in laboratories. It describes the activity of hydrogen ions which determines how acid or alkaline a solution is. The pH value is essential for biological, chemical, and bio-chemical processes, and for the characteristics of many products. The most secure and accurate measurement is done by a pH glass electrode. A sensitive glass membrane detects small voltage changes caused by the hydrogen ions in the sample in comparison to a reference electrode. These voltages are converted to the precise pH values in the meter.