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International standard ISO 2145 defines a typographic convention for the "numbering of divisions and subdivisions in written documents". It applies to any kind of document, including manuscripts, books, journal articles, and standards.
Division and subdivision numbers are cited in written text as in:
… in chapter 4 …
… as lemma 3.4.27 shows …
… the 3rd paragraph in 188.8.131.52 …
In spoken language, the full stops are omitted:
"… in chapter four …"
"… as lemma three four twenty-seven shows …"
"… the third paragraph in two four one seven …"
Support in word processing software
All standard LaTeX document classes generate chapter, section, subsection, figure, table, etc. numbers exactly as defined by ISO 2145.
As of 2003, all Microsoft Word versions are by default set up to add a full stop after the final section number. This does not conform to ISO 2145; however, users can change settings to conform to the ISO standard.