The standard output signal of a glass membrane pH probe is voltage. The voltage generated during measurement is actually the sum of various potentials generated from the glass membrane, reference, liquid junction, and other components that make up the pH sensor. This series of articles looks at the terminology used to define the voltage. Some terms such as slope and zero point are commonly known values that help determine the health of the sensor during the buffer calibration process. Other values such as isopotential point and the asymmetry potential are slight manufacturing deviations that can also factor into the overall accuracy of the measurement.