Editing Calendar date (section)

===Difficulties===
[[File:Memorial to John Etty (18373251064).jpg|thumb|Memorial plaque to John Etty in [[All Saints' Church, North Street, York]], uses [[dual dating]] style to record his date of death as "28 of Jan: {{sfrac|170|8|9}}" ]]
Many numerical forms can create confusion when used in international correspondence, particularly when abbreviating the year to its final two digits, with no context. For example, "07/08/06" could refer to either 7 August 2006 or July 8, 2006 (or 1906, or the sixth year of any century), or 2007 August 6.

The date format of YYYY-MM-DD in ISO 8601, as well as other international standards, have been adopted for many applications for reasons including reducing transnational ambiguity and simplifying machine processing.<ref>{{Cite web |title=International standard date and time notation |url=https://fits.gsfc.nasa.gov/iso-time.html#:~:text=This%20standard%20notation%20helps%20to,traditional%20date%20and%20time%20notations. |access-date=2024-05-01 |website=fits.gsfc.nasa.gov}}</ref> 

An early U.S. [[Federal Information Processing Standard]] recommended 2-digit years. This is now widely recognized as extremely problematic, because of the [[year 2000 problem]]. Some U.S. government agencies now use ISO 8601 with 4-digit years.<ref>{{cite web |title=Date Format for Web site – Information Systems Department Release |date=2002-07-01 |website=Nye County, Nevada |url=http://www.nyecounty.net/iso8601.html |archive-url=https://web.archive.org/web/20080221020451/http://www.nyecounty.net/iso8601.html|archive-date=February 21, 2008}}</ref>{{bsn|reason=It is not clear at what point the piece is copied from elsewhere, so find the original -- possibly by Arthur David Olson at the tz nih archive.|date=November 2023}} 

When transitioning from one calendar or date notation to another, a format that includes both styles may be developed; for example [[Old Style and New Style dates]] in the transition from the Julian to the Gregorian calendar.<ref>{{cite web |last=Spathaky |first=Mike |url=https://www.cree.name/genuki/dates.htm |title=Old Style and New Style Dates and the change to the Gregorian Calendar |access-date=19 August 2023}}. "Before 1752, parish registers, in addition to a new year heading after 24th March showing, for example '1733', had another heading at the end of the following December indicating '1733/4'. This showed where the Historical Year 1734 started even though the Civil Year 1733 continued until 24th March. ... We as historians have no excuse for creating ambiguity and must keep to the notation described above in one of its forms. It is no good writing simply 20th January 1745, for a reader is left wondering whether we have used the Civil or the Historical Year. The date should either be written 20th January 1745 OS (if indeed it was Old Style) or as 20th January 1745/6. The hyphen (1745-6) is best avoided as it can be interpreted as indicating a period of time."</ref>