My ex was an “Executive Secretary” and was proficient in the operation of the “IBM Executive Typewriter”. The IBM Executive was a variable pitch typewriter, meaning that the various letters were a different number of picas wide. Capital “M” being the widest and lower case “i” being the narrowest. There were also several widths of spaces so that the typist could calculate how many picas were needed for each line to be fully justified. Basically a typesetting typewriter that could make a one off letter look like a typeset printed book. All this at 120 WPM with zero errors, as erasures and whiteout were forbidden, as were hyphens.
Watching her type on the thing was mind boggling; she would pre-calculate exactly which width spaces had to be inserted where in a line in order to make the line the proper length… on the fly. When asked how she did it, she couldn’t tell you, she would say she just “knew”. She knew the theory, but couldn’t tell you how she executed it.
It was one of those skills that technology has made obsolete, but demonstrated the power of the human mind, especially on a subconscious level; kind of like basic arithmetic or remembering a friends phone number!