Two Spaces or Not Two Spaces?

Do you remember being told to put two spaces after the end of a sentence? You will, if you grew up in the age before word processing programs on computers. And you may still be doing this today. Just recently, however, I saw this:

How many of you have heard this? I never did until I saw the above image on a  Facebook group for writers.  Typical responses to this post have included people saying that some still do this by habit and that others have stopped using the two spaces.  But some want to still be two-spacers. I guess it's up to you.

Once (probably more than once!) when I was editing my story, I found myself looking for two spaces after sentences.  I then inserted a second space where I'd out only one. This was before I had seen the post above.  Now I think I will have to watch myself to see that I don't do this anymore. But as some of the responders on the Facebook post have said, it's a hard habit to break. I seem to be of that mind. 

I then found this article from 2011. (Apparently this practice has been going on longer than I realized!):

From that article:

Proper protocol is to use ONE SPACE after the period. 

Why? Because of modern typesetting! In olden days typewriters were monospaced, which meant every letter had the same amount of space on either side. But nowadays (unless you are still pecking away on a typewriter) your PC uses proportional fonts. These fonts assign proper spacing between letterforms (also known as "kearning") which is variable depending on what letters or punctuation sit next to each other. This means your computer automatically adjusts for proper space after a period. You no longer need to double space. 

Are you still in the habit of double-spacing? Have you heard this new rule?