Many, many computer users automatically put two spaces after every period, colon, or closing quotation mark, not realizing that the space designed into punctuation already takes into account the extra gap needed after the end of a sentence, so one space, not two, is correct. This has been standard typesetting practice for several hundred years. The Chicago Manual of Style says: "In typeset matter, one space, not two (in other words, a regular word space), follows any mark of punctuation that ends a sentence…" without mentioning the reason. Typeset matter, as a glance at any magazine or book will tell you, is always proportional-spaced. Like I said: you're typesetting, but nobody bothered to tell you.
The Chicago Manual of Style. 15th ed. Chicago: U of Chicago P, 2003.
If you have questions about how to cite sources other than those illustrated here, consult either The Chicago Manual of Style, 16th ed. (Chicago: University of Chicago Press, 2010), or Kate L. Turabian, A Manual for Writers of Term Paper, Theses, and Dissertations, 8th ed. (Chicago: University of Chicago Press, 2013), both of which are available at the Writing Center and in many campus libraries.
The IEEE Computer society prefers the Chicago Manual of Style.
The Chicago Manual of Style was first published in 1906 under the title Manual of Style. It was one of the first guides created to standardize American English manuscript formats for publication. The manual provides guidelines on multiple aspects of creating a polished finished manuscript and is credited with leading the way in standardizing citation style in the bibliography.
The Chicago Manual of Style Online
The Chicago Manual of Style sets the standard for scholarly publishing in the Humanities. Chicago offers two citation formats, the author-date reference format and the standard bibliographic format, each of which provides conventions for organizing footnotes or endnotes, as well as bibliographic citations. Chicago allows scholars accurately and thoroughly to denote and differentiate scriptural, classical, and archival, and other historical sources, as well as to represent the range of multimedia and other new electronic forms of publication.This section contains information on The Chicago Manual of Style method of document formatting and citation. These resources follow the sixteenth edition of The Chicago Manual of Style, which was issued in September 2010.This section contains information on the Chicago Manual of Style method of document formatting and citation. These resources follow the 16th edition of the Chicago Manual of Style, which was issued in September 2010.
Although the 16th edition of The Chicago Manual of Style (2010), which is available online, and the 8th edition of Kate L. Turabian's A Manual for Writers of Research Papers, Theses, and Dissertations, edited by Wayne C. Booth, Gregory G. Colomb, Joseph M. Williams, and the University of Chicago Press Editorial Staff (University of Chicago Press, 2013) also offer guidelines for parenthetical documentation and reference lists, the Chicago and Turabian styles are most commonly thought of as note systems, which are frequently used in history and the arts.