The Beaufort cipher, created by Sir Francis Beaufort, is a substitution cipher that is similar to the Vigenère cipher but uses a slightly modified enciphering mechanism and tableau.
Its most famous application was in a rotor-based cipher machine, the Hagelin M-209
To encrypt (or decrypt), first choose the plaintext character from the top row of the tableau, call this column P.
Secondly, travel down column P to the corresponding key Letter K.
Finally, move directly left from the Key letter to the left edge of the tableau, the CipherText encryption of Plaintext P with Key K will be there.
The Beaufort cipher is a reciprocal cipher, that is, Decryption and Encryption algorithms are the same.
More on Wikipedia: Beaufort Cipher