From Chapter 8, 'Dates, Numbers, Currency, and Weights and Measures'

8.1   Dates

Dates should be given in the form ‘23 April 1564’. The name of the month should always appear in full between the day (‘23’ not ‘23rd’) and the year. No internal punctuation should be used except when a day of the week is mentioned, e.g. ‘Friday, 12 October 2001’. If it is necessary to refer to a date in both Old and New Styles, the form ‘11/21 July 1605’ should be used. For dates dependent upon the time of beginning the new year, the form ‘21 January 1564/5’ should be used. When referring to a period of time, use the form ‘from 1826 to 1850’ (not ‘from 1826–50’), ‘from January to March 1970’ (not ‘from January–March 1970’). In citations of the era, ‘bc’, ‘bce’, ‘ce’, and ‘ah’ follow the year and ‘ad’ precedes it, and small capitals without full stops are used:

54 bc, 54 bce, 622 ce, 1 ah, ad 622

With reference to centuries, all of these, including ‘ad’, follow:

in the third century ad

In references to decades, an s without an apostrophe should be used:

the 1920s (not the 1920’s), the 60s

In references to centuries the ordinal should be spelled out:

the sixteenth century (not the 16th century)

sixteenth-century drama

In giving approximate dates circa should be abbreviated as c. followed by a space:

c. 1490, c. 300 bc

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