This wild looking metal ball embossed with letters was the innovation behind the IBM Selectric Typewriter (13m+ sold).
Normally people don’t care *how* something works, but this mechanism was so unique and interesting looking it because the main highlight of this print ad.
You can see a slow-mo gif of it where in milliseconds it:
Recognizes the letter you hit → Moves the ball to the correct letter → Punches the page
