Double-sided dummy single-needle telegraph used for training operators, made by the General Post Office, British, 1870-1930.

After 1870, when the British telegraph companies were nationalised, needle telegraphs in Britain were standardised on the Morse code, where a movement of the needle to the left indicated a dot, and, to the right, a dash. This simple instrument was developed to train and test operators in the code and uses simple mechanical linkages to work the needles. The student operator would sit on one side of the instrument, while the teacher would sit on the other.