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ABSTRACT
Standard frequency transmissions were first made from the NPL, England, in 1926 to assist E. V. Appleton in his researches on the ionosphere. Subsequently, they were used mainly for the dissemination of a standard of frequency although they have recently contributed to the study of VLF propagation. Now that they are controlled by atomic standards, standard frequency transmissions can be used to give an immediate value of frequency accurate to a few parts in 1011 in any part of the world.