[mad_as_he$$]

Selectrics were not introduced until July, 1961. There were other kinds of electric typewriters before that that provided a power assist operation. I do not recall them being speed sensitive. Old manuals for sure were speed sensitive. My mother could tell who in her typing pool typed something on a manual by how the letters were spaced. Me, I could never see any difference.

[CanaGuy]

Your mother probably also recognized her typist friends' output (on manual typewriters) by character "weight" as well as spacing...weight meaning how black each character was, i.e., the harder you struck a key, the darker the character.

Thus, for a consistent looking document in those days, manual typewriters required that you hit each key with equal force, and steady speed. But that was difficult if you had varying strength in your fingers, and varying speed skills. Novices could often be identified by lighter "a" or "q", versus darker "j" or "f" characters, for example, because of the different strength of the pinky finger vs others, etc.

Also, varying skill and your training could result in having "favorite" keys, versus keys you weren't good or as speedy at.

Also, the alignment of the character hammers would degrade after a while causing spacing errors and characters that were darker on one edge than the other. Some would get so bad as to open up a "O" making it almost a "C". If you see what I mean.

Also, negligent typists, who didn't clean or brush their keys regularly, would suffer ink buildup on the hammers causing a variety of distinctive characteristics.

In summary, a document produced by a manual typewriter is similar to a human fingerprint. Serious investigators can easily match the document to the typewriter and to the typist in an office. A lost art now, methinks.