The paper gives a detailed discussion of the technique of the measurement of the characteristics of cables by the familiar open-end and closed-end method. It is illustrated by reference to the use of the N.P.L. dielectric test-set for those measurements, but is of general application to all measurements made by connection of the cable as a shunt circuit to a closed tuned circuit, with reactance variation as the basis of measurement. The paper is based on practical experience in this work and is intended as a guide for any who have occasion to make this type of measurement.