References
- Albert, A. L., Electrical Communications (John Willey & Sons), 1954, p. 330.
- Vernam, G. S., “Cipher Printing Telegraph Systems for Secret Wire and Radio Telegraphic Communications”, Journal A.I.E.E., XLV (Feb. 1926), pp. 109–15.
- Cohen, A Handbook of Telecommunications (Pitman), 1947, p. 333.
- IBID., Idem, p. 334.
- Siemens & Halske A.G., “The Teleprinter 68 d”. Bulletin No. Fs Bs 2220/1 e (Feb. 1956), pp. 16–18.