- ISO recommends YYYY-MM-DD *using zeros.
- In text, the full date should always be spelled out to avoid ambiguity: 17 May, 1814 (if only year YYYY) (days of week and month names are capitalised).
- Years are expressed in numerals unless they stand at the beginning of a sentence, in which case rewording may be a better option: During 2011 …
- Particular centuries are spelled out and written in lowercase: eighteenth century.
- Decades are either (a) spelled out (as long as the century is clear) and written lowercased, or (b) expressed in numerals. Chicago (2010) AND the Council of Science Editors (CSE) (2006) Style Manuals call for no apostrophe to appear between the year and the s. 2000-2009, 1890s ...
- International System of Units (SI) units are identical for singular and plural
- Spell out name of unit when used in text without an accompanying number
Difference between Chicago and CSE Style Manuals:
Chicago Style Manual: In nontechnical contexts, Chicago advises spelling out whole numbers from zero through one hundred. However, many publications, follow the simple rule of spelling out only single-digit numbers and using numerals for all others.
The Council of Science Editors (CSE): The revised or modern scientific number style treats numbers more consistently by extending the use of numerals to most single-digit whole numbers. *”0 and 1”