The device described, with test results, depends on symmetrical-component principles and consists of two neon tubes in a very simple preset bridge circuit. The phase rotation is shown by the lighting of one of the lamps, the other remaining unlit, and the instrument is superior in this respect, to the traditional Varley method, in which neither lamp is ordinarily completely extinguished. Wide variations of applied voltage are permissible, and a positive indication continues to be given for wider changes in frequency, and for systems which are more unbalanced, than will be encountered in ordinary industrial practice or could be used with orthodox induction-type indicators.The instrument, in effect, determines the relative phase-displacement of the two voltages applied to it and has been used in a more precise form as a phase-angle meter. Only two voltages of the supply system are therefore required, either line or phase values, and satisfactory performance is achieved in practice for polyphase systems for which the device was not specifically designed. The power consumption is small.