Abstract: A lab experiment device and method that demonstrate quantized conductance as a macroscopic gold wire is elongated and broken. The device utilizes a mechanically controlled break junction to demonstrate conductance quantization. A preferred assembly includes a rigid plate with a block to which a micrometer mounts. Spaced posts are mounted to the plate forming a gap between the posts and the block, and a flexible beam is seated against the posts with the anvil of the micrometer seated against the beam. A wire that is mounted to the beam elongates when the anvil forces the beam into a bending configuration. By passing current through the wire and detecting the voltage through a constriction formed in the wire, one can witness conductance quantization as the wire elongates at the constriction to form a conductor of one atom.