Editing 12-hour clock (section)

==Confusion at noon and midnight==
{| align="right" class="wikitable" style="margin: 0 0 1em 1em; font-size: 95%; width: 35em"
|+ Time according to various conventions
|-
!Device or [[style guide|style]]||[[Midnight]]<br /><small>Start of day</small>||[[Noon]]||Midnight<br /><small>End of day</small>
|-
|Written 24-hour time<ref>{{cite book|title = Chicago Manual of Style | at = paragraph 9.41 | edition = 18th | date = 2024 | publisher = University of Chicago Press | isbn=978-0-226-81797-2}}</ref> ||00:00||12:00||24:00 or 00:00 of following day
|-
|[[United States Government Publishing Office|U.S. Government Publishing Office]] (1953)<ref name="GPO1953">{{cite web |url=https://www.govinfo.gov/content/pkg/GOVPUB-GP-6eda8715b8f5cb1d8514325b97334d4f/pdf/GOVPUB-GP-6eda8715b8f5cb1d8514325b97334d4f.pdf |pages=152, 267 |title=United States Government Printing Office Style Manual |date=January 1953 |website=govinfo |publisher=U.S. Government Publishing Office |access-date=5 September 2019 |archive-url=https://web.archive.org/web/20190905161607/https://www.govinfo.gov/content/pkg/GOVPUB-GP-6eda8715b8f5cb1d8514325b97334d4f/pdf/GOVPUB-GP-6eda8715b8f5cb1d8514325b97334d4f.pdf |archive-date=5 September 2019 |url-status=live }}</ref>||12&nbsp;p.m.{{efn|name=startend|These styles are ambiguous with respect to whether midnight is at the start or end of each day.}}||12&nbsp;m.||12&nbsp;p.m.{{efn|name=startend}}
|-
|U.S. Government Publishing Office (2000)<ref name="GPO2000">{{cite web |url=https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2000/pdf/GPO-STYLEMANUAL-2000.pdf |title=U.S. Government Printing Office Style Manual |at=page 156 |website=govinfo |date=2000 |publisher=U.S. Government Publishing Office |access-date=5 September 2019 |archive-url=https://web.archive.org/web/20190905160112/https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2000/pdf/GPO-STYLEMANUAL-2000.pdf |archive-date=5 September 2019 |url-status=live }}</ref>||12&nbsp;p.m.{{efn|name=startend}}||12&nbsp;a.m.||12&nbsp;p.m.{{efn|name=startend}}
|-
|U.S. Government Publishing Office (2008)<ref name="GPO2008">{{cite web|url=https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2008/pdf/GPO-STYLEMANUAL-2008.pdf|title=U.S. Government Printing Office Style Manual|page=271|website=govinfo|date=2008|publisher=U.S. Government Publishing Office|access-date=5 September 2019|archive-url=https://web.archive.org/web/20190412235057/https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2008/pdf/GPO-STYLEMANUAL-2008.pdf|archive-date=12 April 2019|url-status=live}}</ref>||12&nbsp;a.m.{{efn|name=startend}}||12&nbsp;p.m.||12&nbsp;a.m.{{efn|name=startend}}
|-
|Japanese legal convention<ref>{{cite web |script-title=ja:午前１２時？ 午後０時？ |trans-title=12&nbsp;AM? or 0&nbsp;PM? |url=http://jjy.nict.go.jp/QandA/FAQ/12am-or-0pm-J.html |date=15 February 1989 |website=[[National Institute of Information and Communications Technology]] |language=ja |access-date=24 May 2017 |archive-url=https://web.archive.org/web/20170606032129/http://jjy.nict.go.jp/QandA/FAQ/12am-or-0pm-J.html |archive-date=6 June 2017 |url-status=dead}}</ref>||{{lang|ja|午前0時}}<br />(0&nbsp;a.m.)
|{{lang|ja|午前12時}}<br />(12&nbsp;a.m.)
|{{lang|ja|午後12時}}<br />(12&nbsp;p.m.)
|-
|Japanese common usage<ref name="NAO Japan">{{cite news |script-title=ja:質問4-1）正午は午前12時？それとも、午後12時？ |trans-title=Question 4-1) Is noon 12&nbsp;a.m.? Or 12&nbsp;p.m.? |url=https://www.nao.ac.jp/faq/a0401.html |website=[[National Astronomical Observatory of Japan ]] |language=ja |access-date=19 January 2022  }}</ref>||{{lang|ja|午前0時}}<br />(0&nbsp;a.m.)
|{{lang|ja|午後0時}}<br />(0&nbsp;p.m.)
|{{lang|ja|午後12時}}<br />(12&nbsp;p.m.)
|-
|[[Canadian Press]],<ref name="CP" /> UK standard<ref name="NPL" />||midnight||noon||midnight
|-
|Associated Press style<ref name="AP">Paula Froke, Anna Joe Bratton, Oskar Garcia, Jeff McMillan & Jerry Schwart, Eds., 54th ed., ''The Associated Press Stylebook and Briefing on Media Law'', New York: Basic Books, June 2019, {{ISBN|978-1-5416-9989-2}}, s.v. noon, midnight, times.</ref>||—||noon||midnight
|-
|[[National Institute of Standards and Technology|NIST]]<ref name="NISTFAQ" />||midnight{{efn|name=niststartend|NIST recommends using 11:59&nbsp;p.m. and 12:01&nbsp;a.m. to disambiguate when needed.}}<br />12:01&nbsp;a.m.||noon||midnight{{efn|name=niststartend}}<br />11:59&nbsp;p.m.
|-
|colspan="4"|{{noteslist}}
|}

It is not always clear what times "12:00&nbsp;a.m." and "12:00&nbsp;p.m." denote. In [[Latin]], ''{{Lang|la|ante meridiem}}'' (a.m.) means "before midday" and ''{{Lang|la|post meridiem}}'' (p.m.) means "after midday". Since noon is neither before nor after itself, the terms a.m. and p.m. do not apply.<ref name=NISTFAQ /> Although noon could be denoted "12&nbsp;m.", this is seldom done<ref name="chicago">{{cite book|title = Chicago Manual of Style | at = paragraph 9.40 | edition = 18th | date = 2024 | publisher = University of Chicago Press | quote = Although noon can be expressed as 12:00 m. (m = ''meridies''), very few use that form. | isbn=978-0-226-81797-2}}</ref> and also does not resolve the question of how to indicate midnight.

By convention, "12&nbsp;a.m." denotes midnight and "12&nbsp;p.m." denotes noon.<ref name="AHDEL">{{cite dictionary|url=http://ahdictionary.com/word/search.html?q=AM|title=AM|archive-url=https://web.archive.org/web/20140109230904/http://ahdictionary.com/word/search.html?q=AM|archive-date=9 January 2014|url-status=live|dictionary=[[The American Heritage Dictionary of the English Language]]|edition=Fifth|date=2011}}</ref>
However, many style guides recommend against using either because of the potential for confusion. Many recommend instead using the unambiguous terms "12&nbsp;noon" and "12&nbsp;midnight", or simply "noon" and "midnight". These include ''[[The American Heritage Dictionary of the English Language]]'',<ref name="AHDEL" />
''The Canadian Press Stylebook'',<ref name="CP">{{cite book|title=The Canadian Press Stylebook|edition= 11th |date = 1999 | at = page 288}}</ref>
and the [[National Institute of Standards and Technology|NIST]]'s "Frequently asked questions (FAQ)" web page.<ref name=NISTFAQ>{{cite web|url=https://www.nist.gov/pml/time-and-frequency-division/times-day-faqs|title=Times of Day FAQs |publisher=[[National Institute of Standards and Technology]]|date=21 September 2016|access-date=30 September 2018|archive-url=https://web.archive.org/web/20180921153333/https://www.nist.gov/pml/time-and-frequency-division/times-day-faqs|archive-date=21 September 2018|url-status=live}}</ref>

Alternatively, some recommend referring to one minute before or after 12:00, especially when referring to midnight (for example, "11:59&nbsp;p.m." or "12:01&nbsp;a.m."). These include the UK's [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]] "FAQ-Time" web page.<ref name="NPL">{{Cite web |url=http://www.npl.co.uk/science-technology/time-frequency/time/faqs |title=National Physical Laboratory, ''FAQ-Time'' |access-date=11 January 2015 |archive-url=https://web.archive.org/web/20150303095129/http://www.npl.co.uk/science-technology/time-frequency/time/faqs/ |archive-date=3 March 2015 |url-status=dead }}</ref>
That has become common in the United States in legal contracts and for [[airplane]], [[bus]], or [[train]] schedules, though some schedules use other conventions. Occasionally, when trains run at regular intervals, the pattern may be broken at midnight by displacing the midnight departure one or more minutes, such as to 11:59&nbsp;p.m. or 12:01&nbsp;a.m.<ref>{{cite web|url=http://www.abelliogreateranglia.co.uk/f/62130/62130.pdf|title=Cheshunt/Enfield Town to London Liverpool Street via Seven Sisters service Interim train timetables|archive-url=https://web.archive.org/web/20150526154117/http://www.abelliogreateranglia.co.uk/f/62130/62130.pdf|archive-date=26 May 2015|url-status=dead|website=Abellio Greater Anglia London|date=17 May 2015|pages=7,8}}</ref>

Some authors have been known to use the reverse of the normal convention. E. G. Richards in his book ''Mapping Time'' (1999) provided a diagram in which 12&nbsp;a.m. means noon and 12&nbsp;p.m. means midnight.<ref>{{cite book|last=Richards|first=E. G.|title=Mapping Time: the Calendar and its History|publisher=[[Oxford University Press]]|date=1999|page=289}}</ref>
Historically, the style manual of the [[United States Government Printing Office]] used 12&nbsp;a.m. for noon and 12&nbsp;p.m. for midnight, though this was reversed in its 2008 editions.<ref name="GPO2000" /><ref name="GPO2008" />

In [[Date and time notation in Japan|Japanese usage]], midnight is written as {{lang|ja|午前0時}} (0&nbsp;a.m.) and noon is written as {{lang|ja|午後0時}} (0&nbsp;p.m.), making the hours numbered sequentially from 0 to 11 in both halves of the day. Alternatively, noon may be written as {{lang|ja|午前12時}} (12&nbsp;a.m.) and midnight at the end of the day as {{lang|ja|午後12時}} (12&nbsp;p.m.), as opposed to {{lang|ja|午前0時}} (0&nbsp;a.m.) for the start of the day, making the Japanese convention the opposite of the English usage of 12&nbsp;a.m. and 12&nbsp;p.m.<ref name="NAO Japan" />