Conductivity is the ability of a material to conduct electric current. The principle by which instruments measure conductivity is simple two plates are placed in the sample, a potential is applied across the plates (normally a sine wave voltage), and the current that passes through the solution is measured. Conductivity (G), the inverse of resistivity (R), is determined from the voltage and current values according to Ohm's law.

Potentiometric pH meters measure the voltage between two electrodes and display the result converted into the corresponding pH value. They comprise a simple electronic amplifier and a pair of electrodes, or alternatively a combination electrode, and some form of display calibrated in pH units.