This document is concerned with reporting the state of the art of measuring impedance in distributed parameter coaxial waveguide systems, propagating a TEM wave. Coaxial lines can be used from direct current to above 40 gigahertz, but are widely utilized beginning with the audio frequencies up through 18 gigahertz. Considered are available accuracies from 50 megahertz to 16 gigahertz, general prin...