Information from the following sources was used for this section.
Cryptograph (coding and decoding machine) by Sir Charles Wheatstone, 1843-1875 – Science Museum
Wheatstone Cryptograph – Crypto Machines pages
Several Machine Ciphers and Methods for their Solutions (1918) – Friedman, William F., Riverbank publications No 20
The Scientific Papers of Sir Charles Wheatstone (1879) – Wheatstone, Charles, collected and published by The Physical Society of London
A Charles Wheatstone Cryptograph – Bonhams
The Mystery of Colonel Decius Wadsworth’s Cipher Device (1982) – Kruh, Louis (Cryptologia, 6:3)