The letters relate to many facets of this subject, for example the clocks from which the signals were derived, the frequencies used in broadcasting and the accuracy of the signals. The period covered by this correspondence was one of great technical advances in time-keeping within the Royal Observatory (RO) and there are many letters toward the end of the files giving information of these developments.

At the beginning, i.e. in 1916, the only radio time signals available were the rather primitive spark emissions from the Eiffel Tower, Paris, and the reception equipment was equally crude. In the 1920s there were great improvements in radio technology, both in transmission and in reception, while at the same time there was a considerable growth in the number of time signal transmissions. This correspondence reflects these changes and the interest they engendered.

During the Second World War the correspondence is mainly confined to information exchanges within the UK with the Post Office, National Physics Laboratory and Admiralty. Following the end of the war, there was a great increase in correspondence nearly all of which was due to the re-establishment of relations with foreign observations.