Oxygen Sensor System for Determining Active Oxygen Levels in Molten Metal Comprising a Probe for Immersion into a Bath of Molten Metal, a Holder for Supporting the Probe, and a Recorder for Displaying or Recording Readings of the Probe; Sampling System Capable of Immersion into Molten Metal for Obtaining a Sample of Molten Metal, Comprising a Filling Tube and Chamber, One of which Contains a Deoxidant; Instrument for Determining Carbon Content of Molten Metal; Digital Oxygen Analyzer; Carbon Percentage Sensor System for Determining the Percentage of Carbon in Molten Metal Comprising a Probe for Immersion into a Bath of Molten Metal, a Holder for Supporting the Probe, and a Recorder for Displaying or Recording Readings of the Probe