One Space or Two?

Q. Please help. I have confusion regarding the correct spacing after periods and other closing punctuation. My company uses the font Arial and consistently uses a flush-left margin. We are an engineering company. My job consists in preparing documents and letters for customers. Everything I read in manuals and from technical writers directs me to use one space after periods. I find that it works very well, except occasionally, when an extra space helps readability. Knowledgeable engineers have embraced the one space use as being consistent with the font design and automation of reports. Others are unpleased with the one space, they think they have difficulty reading. (I, too, had an adjustment period which I forced myself to endure until it became automatic to read easily.) We are preparing technical information. What do you think? Thanks for your wonderful support and especially the quick answers. I greatly appreciate your service.

A. Published work these days rarely features two spaces after a period. In the era when type was set by hand, it was common to use extra space (sometimes quite a bit of it) after periods, a practice that continued into the first half of the twentieth century. And many people were taught to use that extra space in typing class. But introducing two spaces after a sentence-ending period—and only after those periods—causes problems. Absolute consistency is easy to monitor when double spaces are never allowed, but less easy when some spaces after periods are double and others single (such as those at the ends of abbreviations and initialisms in running text). Since there is no proof that an extra space actually improves readability—as your comment suggests, it’s probably just a matter of familiarity—CMOS follows the industry standard of one space after a period.