Abstract: A method and apparatus for displaying the active oxygen content of a liquid metal and the sensor temperature of a probe from signals developed by the probe which is capable of being plunged directly into the liquid metal. The probe comprises a small mass of solid oxygen-permeable electrolyte in the end of a refractory insulating tube, an oxygen reference material in contact with the inner surface of the electrolyte, and suitable electrodes for providing both a signal representative of the active oxygen of the liquid metal and a signal representative of the sensor temperature. The apparatus comprises first recording means for displaying the sensor temperature, and second recording means for displaying the active oxygen of the metal, a source of power, and sequencing means which are initially responsive to the probe emf for sequencing the operation of the apparatus.