Double-sided telegraph used for training operators, 1870-1930.
© Science Museum / Science & Society Picture Library
Dummy double-sided single-needle telegraph used for training operators. By about 1870 needle telegraphs in Britain had 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.