One Space or Two?

I recently learned (via Facebook, of course) that I was out of the loop on my typing rules. Some time since sixth grade type class with Mr. Rowan (and ninth grade type with Mrs. Jessop - how many hours did we spend learning to type), the rules have changed. I no longer should type two spaces after a period. Lest you think I accept everything on Facebook as truth, I did some further research.

From Grammar Girl (http://grammar.quickanddirtytips.com/spaces-period-end-of-sentence.aspx):
Two Spaces After a Period--The Old Way

Here's the deal: Most typewriter fonts are what are called monospaced fonts. That means every character takes up the same amount of space. An "i" takes up as much space as an "m," for example. When using a monospaced font, where everything is the same width, it makes sense to type two spaces after a period at the end of a sentence to create a visual break. For that reason, people who learned to type on a typewriter were taught to put two spaces after a period at the end of a sentence. 

One Space After a Period--The New Way

But when you're typing on a computer, most fonts are proportional fonts, which means that characters are different widths. An "i" is more narrow than an "m," for example, and putting extra space between sentences doesn't do anything to improve readability.

Notice how in this example, the "i's" and "t" take up much less space in the proportional font than they do in the monospaced font.

Although how many spaces you use is ultimately a style choice, using one space is by far the most widely accepted and logical style. The Chicago Manual of Style (1), the AP Stylebook (2), and the Modern Language Association (3) all recommend using one space after a period at the end of a sentence. Furthermore, page designers have written in begging me to encourage people to use one space because if you send them a document with two spaces after the periods, they have to go in and take all the extra spaces out.

I know it's a hard habit to break if you were trained to use two spaces, but if you can, give one space a try

And from Slate (http://www.slate.com/articles/technology/technology/2011/01/space_invaders.html):

Every modern typographer agrees on the one-space rule. It's one of the canonical rules of the profession, in the same way that waiters know that the salad fork goes to the left of the dinner fork and fashion designers know to put men's shirt buttons on the right and women's on the left. Every major style guide—including the Modern Language Association Style Manual and the Chicago Manual of Style—prescribes a single space after a period. (The Publications Manual of the American Psychological Association, used widely in the social sciences, allows for two spaces in draft manuscripts but recommends one space in published work.) Most ordinary people would know the one-space rule, too, if it weren't for a quirk of history. In the middle of the last century, a now-outmoded technology—the manual typewriter—invaded the American workplace. To accommodate that machine's shortcomings, everyone began to type wrong. And even though we no longer use typewriters, we all still type like we do. (Also see the persistence of the dreaded Caps Lock key.)

I guess I'll be breaking a habit. Here's to one space. I'll let you know when I'm back up to my 100+ wpm with one space. I'm sure it will slow me down for a while.