The inventive optical device for measuring the thickness of a medium which is at least partially transparent for an incident beam and covers a second medium comprises a laser for generating the light incident beam in such a way that a beam reflected by the first medium surface and a beam scattered by the second medium surface are formed. The distributed network switch is divided into logical switch partitions, or logical networks, that may share a routing table. An RFID tag is affixed with the object that is to be located. An inspection opening 31 with a door 32 is provided in a furnace wall surface 37W to open into the molten metal processing portion.