Abstract: An ion measuring device (pH meter) is adapted to store and discharge standardizing solution, as well as to provide measurements of the hydrogen or other ion concentrations of unknown samples; the device including a working electrode of known construction and a reference electrode adjacent to the working electrode; and further including at least one storage reservoir for containing a standardizing solution, and a measuring or standardizing chamber located at the lower end of the reservoir with means, preferably in the form of a valve, for permitting communication between the reservoir and standardizing chamber such that standardization and calibration can be carried out.