I'm just old enough to remember using a typewriter for school work. And at least on the typewriter I used, the period key produced a width of exactly a period.

I'm just old enough to remember using a typewriter for school work. And at least on the typewriter I used, the period key produced a width of exactly a period. In other words, an extra space was absolutely required just to "fill out" the period. And the small period width allowed you to do a "proper" ellipsis. I didn't quite realize that was the reason for the double space until these comments, though, as we were simply taught that it was required to put 2 spaces after a period. The comma, btw, was slightly wider.