The pH measurement is a relative measurement that merely indicates the pH difference between a standard solution and an unknown solution. The actual measurement requires periodic calibration with a standard buffer solution. Therefore, in order to achieve consistent values, a pH scale must be established. The pH scale is scaled from 0 to 14 pH and the magnitude of the pH scale is determined by the pHs of the reference buffer solution.
Therefore, the meaning of the pH scale can be expressed as follows: According to the pH definition, several pH buffer solutions are selected as the fixed points of the pH scale in the range of 0 to 14 pH, and their pHs are measured by the most accurate method that can be achieved in the contemporary art value. Internationally, there are two kinds of pH scale, that is, a variety of reference pH scale and a single standard pH scale, China uses a variety of benchmark pHs scale.