In the present paper a brief description of some of the work carried out in the Research Section of the British Post Office is given. Part 1 is devoted ot electro-accustic and various voice-ear measurements on microphones and receivers are described. Part 3 deals with some mechanical tests by means of which rapid acceptance tests and esticmates of the commercial life of instruments can be made. The question of the measurement of the efficiency of apparatus and circutis in acutal use is discusse in Part 4.