I was helping my daughter with a paper today when the topic of the proper spacing after a period came up. I told her she needed a double space after a period and she looked at me increduluosly and said, "why?" Certain I was right, I googled the question only to find out, much to my surprise, I was wrong! Apparently the double space after the period is a convention dating to use of manual typewriters. Since the advent of word processing programs and proportional fonts, the convention of the double space is obsolete. A single space is used instead, but word processing programs do allocate a little extra space automatically. I had no idea.