In 1870 Émile Baudot created a code for telegraphy that used bits in place of dot and dashes. That allowed more words per minute to be transmitted than was possible with morse code.
With Baudot code machines could be built that would automatically decode the signal and type it out as plain english. This technology would be called the teletype machine.
Teletype machines still used this code or variation until they were replaced over a century later.
This is also where the term Baud rate comes from.
Why not "cels?"
I mean I usually just say e.g. "30C" instead of "30 degrees celsius"
I usually just say 30 degrees. 😁
People say "30F," too.
But how do we decide when someone's memorial name should be shortened?