Re your comparison of type on post #101, do you have a comment on the evenness of the lines of type. Did the IMB selectrics have perfect horizontal agreement, as computers do? Or were their words 'wavy' with various letters not perfectly evenly hitting the paper like manual typewriters? Sorry, I cannot explain any better what I am asking.
A good question. One of the nice things about the IBM Selectrics was that the ball action was very quick, and the ball would return to the line in time to keep the typing line straight, unless the typist was very fast. Since the ball rotates and moves up and down with each character, as opposed to a traditional arm-type typewriter, which only moves up and down on the SHIFT key, the motion had to be extremely quick.
An extremely fast typist (90 wpm or better, which was fast in those days) could occaisionally get an off line character, but not often. A hunt-and-peck type would never do so.
So the Selectrics were good. Not as perfect as a laser printer, but good.
The better Selectrics looked like typsetting. Not perfect, but very good.