During World War II, codebooks were only used each day to set up the rotors, their ring settings and the plugboard. For each message, the operator selected a random start position, let's say "WZA", and a random message key, perhaps "SXT". He moved the rotors to the "WZA" start position and encoded the message key "SXT". Assume the result was "UHL". He then set up the message key, "SXT", as the start position and encrypted the message. Next, he transmitted the start position, "WZA", the encoded message key, "UHL", and then the ciphertext. The receiver set up the start position according to the first trigram, "WZA", and decoded the second trigram, "UHL", to obtain the "SXT" message setting. Next, he used this "SXT" message setting as the start position to decrypt the message. This way, each ground setting was different and the new procedure avoided the security flaw of double encoded message settings.