One of the first devices for encryption was the cipher disk. These are two round metal discs that sit on a common axis and are connected in such a way that the smaller one can rotate on the larger one. Discs of this type have been around since the 15th century. The development of the first cipher disk is attributed to Leon Battista.
Different alphabets or symbols are indicated on the outer edge of each disk. By turning the disks against each other, these alphabets shift, which is used for encryption. Here, the outer disk contains the ciphertext alphabet and the inner one the plaintext alphabet.
Thus, after setting the disks once, a monoalphabetic encryption can be achieved very easily, or, if the position of the disks to each other is changed during encryption, even a polyalphabetic encryption.