It has been mentioned earlier that the telecommunication connections were bad. But it was not only single characters that were distorted and therefore gave an opening for breaking.
The abundant number of ``parallel texts'', that is an enciphered text sent several times with the same key setting on the cipher machine, were a big help in breaking the Geheimschreiber. In extreme cases the same message was sent 20 to 40 times with the same setting. How could this happen? One of the basic rules of cryptological security is never to send the same or a different message with the same key setting. Bad connections and distortions together with laziness gave many openings of this type.
The keying procedures have already been described. It takes a certain time to adjust the wheels by hand. To facilitate the adjustment of the ``QEK-wheels'', that is the current key for the day, there existed a cursor that easily could be moved around on the wheel and positioned on an arbitrary key number.
The wheels could be freed with a locking arm. All the wheels could be turned backwards with a handle until their cursors came to a home position when the wheel stopped. This handle sat on the right on the front of the machine under a plate with the inscription ``LANGSAM DREHEN'' (turn slowly). The idea was that every morning the cursors would be set on the five wheels that were intended for the daily key (the QEK-wheels). Later these wheels could quickly be returned to their agreed positions before every new transmission. Unfortunately it became a habit that even when the ``QEP-numbers'' were set, the cursors were set to the key values and then the wheels were cranked back. This was against the existing rules, as new ``QEP-numbers'' should be selected for every new message.
Since the lines were long and sometimes poor there were often distortions. These sometimes caused one of the machines to interpret the distortion as a character. The operator of the other machine would not notice anything. One of the machines would then be one step ahead of the other. The cipher machines were no longer in phase and the message became unintelligible. When this happened, it was necessary to break the transmission, switch over to plaintext, choose a new message key and continue the transmission.
Now the big mistake was made. For each break in the transmission of a message due to continuous distortions on the line, the operators chose the easy solution of simply cranking back the wheels to the previous setting. In this way the cryptanalysts got their parallel texts with all their errors and flaws which gave a large number of opportunities for breaking it. The high security of the Geheimschreiber became therefore in many ways simply illusory.