Abstract: A sonde is provided which includes a plurality of discrete sensing electrodes of analog output projecting from a housing within which are accommodated a micro-processor and an analog-digital converter to digitize the output of the electrodes. A stirrer is fully integrated into the housing and projects from the housing centrally with the electrodes around it. The stirrer motor and the stirrer control are integrated into the housing. The micro-processor controls the stirrer control. The sonde also has a readily attachable and detachable calibration cup with wells defined therein. Each well is designed to receive its own liquid. The calibration cup is designed such that all the electrodes can be calibrated simultaneously.