It is surprising how small items that have been over looked, can completely bring a computer system to its knees. Back in the late 1960,s telegraph systems were stating to be automated, by telecoms companies as well as in private ones (BA and Shell being some of the first).
The start of a message started with the code ZCZC and the ended with NNNN, a problem arose one day when someone put in a message …. (Four full stops). Full stop on a teleprinter is the uppercase of N, thus the computer considered the four full stops as the end of message code. As the code for N and full stop are the same (Space, Space, Mark, Mark, Space, if I have got it right after 40 years). So it stopped the transmission and sent an error message to the engineers, as it could not understand were the ZCZC for the next message was.
The answer was to instruct teleprinter operators to insert between each full stop, the figure shift code for upper case. Therefor the computer would not think it was seeing Four N’s on the trot and the problem was solved.
Now some of you will know why you had ZCZC and NNNN on your telegrams.