Do you type one or two spaces after a period in a sentence? What were you taught?
I was taught to use two spaces, but I never realized that type setters are adamant about the use of one space between sentences. After forty years of writing, I find it extremely difficult not to double-space after a period. As I write this post, I am having difficulty not putting two spaces after typing that period. See? I did it again.
Anyway, check out this article for a history of the two vs. one space rule and the rationale for the latter.