Editing Microsoft Excel (section)

=== Fictional leap day in 1900 ===
Excel includes February 29, 1900, incorrectly treating 1900 as a [[leap year]], even though e.g. 2100 is correctly treated as a non-leap year.<ref>{{cite web|url=http://support.microsoft.com/kb/214058/en-us|title=Days of the week before March 1, 1900 are incorrect in Excel|publisher=Microsoft|access-date=November 10, 2008|archive-url=https://archive.today/20120714062344/http://support.microsoft.com/kb/214058/en-us|archive-date=July 14, 2012|url-status=live}}</ref><ref>{{cite web|url=https://docs.microsoft.com/office/troubleshoot/excel/wrongly-assumes-1900-is-leap-year|title=Excel incorrectly assumes that the year 1900 is a leap year|publisher=Microsoft|access-date=May 1, 2019|archive-date=June 7, 2023|archive-url=https://web.archive.org/web/20230607133954/https://learn.microsoft.com/en-ca/office/troubleshoot/excel/wrongly-assumes-1900-is-leap-year|url-status=live}}</ref> Thus, a formula counting dates between (for example) February 1, 1900 and March 1, 1900 will return an incorrect result. The bug originated from [[Lotus 1-2-3]], where it was deliberately implemented to save computer memory, and was also intentionally implemented in Excel for the purpose of [[bug compatibility]].<ref>{{cite web|url=http://www.joelonsoftware.com/items/2006/06/16.html|title=My First BillG Review|first=Joel|last=Spolsky|publisher=Joel on Software|date=June 16, 2006|access-date=November 10, 2008|archive-date=June 7, 2008|archive-url=https://web.archive.org/web/20080607153522/http://www.joelonsoftware.com/items/2006/06/16.html|url-status=live}}</ref> This legacy has later been carried over into Office Open XML file format.<ref name="The Contradictory Nature of OOXML">{{cite web|url=http://www.consortiuminfo.org/standardsblog/article.php?story=20070117145745854|title=The Contradictory Nature of OOXML|date=January 17, 2007|publisher=ConsortiumInfo.org|access-date=September 23, 2009|archive-date=August 18, 2009|archive-url=https://web.archive.org/web/20090818095243/http://www.consortiuminfo.org/standardsblog/article.php?story=20070117145745854|url-status=live}}</ref>