I was manually typing in a long serial number into an email, and I thought how nice is it that the email never picks up errors just from being transmitted through the Internet. Computers & servers are at least good at that.
However, if it was the late-19th century and I wanted to send you something like that via a telegram, would I have been worried that it could be garbled up in transmission by the operators? How did telegram services avoid this but still be able to have mass service? Just a single letter or number off could be really bad in some circumstances.
Thank you!
Your are correct in thinking that it might have been bad for there to be errors in a telegraphed message. Not so much for the one that reads " Mother will be home Dec 23" but the one that says that the rail track from Baltimore to York is clear of trains! As a result, accuracy in both sending and receiving was prized- it was much more important to send code clearly than to send it fast.
But the operators were lucky, in that what they were having was really more of a conversation. As the sender was coding, the receiver was writing it down- typically, copying behind- storing up a few words in his head as he decoded them, then writing them down. If the sender made a mistake and knew it, he could insert a correction- if the date he coded was wrong, for example, he could then code "date;" and fill in the correct one. If the receiver didn't catch something, or made a mistake in writing, he could break into the transmission and ask for it again, sending the last word he got correctly. He could even type "ga ahr" , which meant, send it all again. If the sender was not sure if the receiver was copying, he could code "u tr", ( are you there?) and the receiver would reply "I", which also stood for "yes sir".
There were also many abbreviations: "hw sun wi 1st 74 b rdy" stood for "How soon will 1st No. 74 be ready?". And there were also rules: by the 1860's, trains were generally dispatched with telegraphed orders. A train about to leave a station would first have orders telegraphed to proceed to the next, and that station would reply when the train was leaving. Just like in aviation, absolute clarity was essential to avoid confusion, and just like in aviation, opening a message, addressing it, closing it, signalling it had been received, etc. all obeyed strict formulae.
Also, an experienced operator could eventually send and receive pretty quickly. It really became another language in which they could become quite fluent. Although ham radio licenses no longer require Morse code ability, there are plenty of hams who know it still. After a while, they can often tell the identity of another sender just by his/her "fist", their individual way of coding.
George M Dodge : The Telegraph Instructor