Andrew Carnegie
Andrew Carnegie learned telegraphy by heart.
In 1849, Carnegie became a telegraph messenger boy in the Pittsburgh Office of the Ohio Telegraph Company, at $2.50 per week ($94 by 2024 inflation) following the recommendation of his uncle. He was a hard worker and would memorize all of the locations of Pittsburgh's businesses and the faces of important men. He made many connections this way. He also paid close attention to his work and quickly learned to distinguish the different sounds the incoming telegraph signals produced. He developed the ability to translate signals by ear, without using the paper slip. Within a year he was promoted to an operator.