[Juke2]

I guess your point depends upon what you mean by "common use".

I was certainly using an IBM typewriter, with proportional pitch type-balls by 1969. At the time, I was working at a very low-budget publication, where most of the staff never drew a salary. We could afford the typewriter, though.

I don't think you've actually caught anything here.

[Buckhead]

I think you are mistaken. There is ample research on this point at the thread referenced just above. The Selectric used monospaced fonts, but could vary between 10 and 12 cpi, which was referred to as "pitch." To get proportionally spaced fonts you had to get an IBM Selectric Composer, and it was a very expensive machine for typesetting to get documents camera ready. You had to type each line twice and fiddle with knobs and so forth. One mistake and your were screwed and had to start over. There is no frigging way the TANG used a Selectric Composer for personal memos to file. Plus, these memos have superscript, which was not available in that form at that time, and the signatures don't match. It goes on and on.

[tallhappy]

I was certainly using an IBM typewriter, with proportional pitch type-balls by 1969. At the time, I was working at a very low-budget publication, where most of the staff never drew a salary. We could afford the typewriter, though.

I don't think you've actually caught anything here.

Fantastic insight juke2. Dan Rather is desperately trying to contact you.

Sorry, couldn't help myself...

[MonroeDNA]

"I was certainly using an IBM typewriter, with proportional pitch type-balls by 1969..."

I think you are mistaken.

"Proportional pitch" in ball-type writers would require that every letter had a different mechanical pitch. Incredible machining required, such that the said ball would likely cost around $30,000 today.