Scott, J. M. (1972). Extel 100: The centenary history of the exchange telegraph company. London: Ernest Benn Limited.
Παραπομπή Chicago StyleScott, J. M. Extel 100: The Centenary History of the Exchange Telegraph Company. London: Ernest Benn Limited, 1972.
Παραπομπή MLAScott, J. M. Extel 100: The Centenary History of the Exchange Telegraph Company. London: Ernest Benn Limited, 1972.
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