Indication of a measured quantity at a distance from the point where the measurement is carried out has become of great importance, in view of the modern practice of centralized control. At the control point, indications must be given of all quantities necessary for the efficient operation of the system, and thus remote indication is essential. This paper deals with the principles on which some electrical methods of remote indications are based. Numerous systems have been developed, in all parts of the world, and for purposes of description they may be classified according to the fundamental principles on which they are based. A description is given of at least one system in each class indicating various applications of the general principle of the class. The conditions under which an equipment is to be used, and the characteristics of the various systems, will determine which of the numerous methods described should be chosen for a particular application.