Abstract: Microwave transmission and reception, and analysis thereof, are used to monitor the level of molten metal, paradigmatically steel, in a tundish receiving molten metal (steel) from a ladle or other vessel and passing it to the head of a continuous caster, while the steel in the tundish is covered with slag. The control factors may include level, weight or volume limits in the tundish derived from historical or real-time data, including data representing a predictable or developing vortex in the well feeding the continuous caster. The system is particularly useful in minimizing transition mix during change from one metal specification or grade to another.