Editing Week (section)

===Other week numbering systems===
In some countries, though, the numbering system is different from the ISO standard. At least six numberings are in use:<ref>{{cite web |url=http://www.pjh2.de/datetime/weeknumber/wnd.php?l=en |title=Weeknumber sorted by definition |author=Peter Johann Haas |date=26 January 2002 |website=pjh2.de |access-date=3 April 2015 |archive-date=9 February 2016 |archive-url=https://web.archive.org/web/20160209193500/http://www.pjh2.de/datetime/weeknumber/wnd.php?l=en |url-status=dead }}</ref><ref>{{cite web |url=http://www.merlyn.demon.co.uk/weekinfo.htm |title=Calendar Weeks |publisher=J. R. Stockton |url-status=usurped |archive-url=https://web.archive.org/web/20140113000828/http://www.merlyn.demon.co.uk/weekinfo.htm |archive-date=13 January 2014}}</ref> {{Dubious|date=October 2015}}

{|class="wikitable"
! System
! First day of week
!colspan="3"| First week of year contains
!Can be last week of previous year
! Used by or in
|-
| ISO 8601 || [[Monday]] || {{nowrap|4 January}} || {{nowrap|1st Thursday}} || {{nowrap|4–7 days of year}} || align=center | yes || EU (exc. Portugal) and most of other European countries, most of Asia and Oceania
|- 
| Middle Eastern || [[Saturday]] || {{nowrap|1 January}} || {{nowrap|1st Friday}} || {{nowrap|1–7 days of year}} || align=center | yes || Much of the Middle East
|-
| Western traditional || [[Sunday]] || {{nowrap|1 January}} || {{nowrap|1st Saturday}} || {{nowrap|1–7 days of year}} || align=center | yes || Canada, United States, Iceland, Portugal, Japan, Taiwan, Thailand, Hong Kong, Macau, Israel, Egypt, South Africa, the Philippines, and most of Latin America
|-
| [[Broadcast Calendar]] || [[Monday]] || {{nowrap|1 January}} || {{nowrap|1st Sunday}} || {{nowrap|1–7 days of year}} || align=center | yes || Broadcast services in the United States<ref>{{Cite web|title=Broadcast Calendars {{!}} RAB.com|url=http://www.rab.com/public/reports/broadcastCalendar.cfm?type=nm|access-date=26 May 2021|website=www.rab.com}}</ref>
|}

Because the week starts on either Saturday, Sunday, or Monday in all these systems, the days in a [[workweek]], Monday through Friday, will always have the same week number within a calendar week system. Quite often, these systems will agree on the week number for each day in a workweek:

* In years where 1 January is a [[Common year starting on Monday|Monday]], [[Common year starting on Tuesday|Tuesday]], [[Common year starting on Wednesday|Wednesday]], or [[Common year starting on Thursday|Thursday]], all of the above week numbering systems will agree. 
* [[Common year starting on Friday|In years where 1 January is a Friday]], ISO-8601 will be different, but the rest will agree. 
* [[Common year starting on Saturday|In years where 1 January is a Saturday]], ISO-8601 and the Middle Eastern system will agree, being different from Western Traditional and the Broadcast Calendar which will agree. 
* [[Common year starting on Sunday|In years where 1 January is a Sunday]], the Broadcast Calendar will be different, but the rest will agree.

Note that this agreement occurs only for the week number of each day in a work week, not for the day number within the week, nor the week number of the weekends.

{{anchor|Epidemiology}}The '''epi week''' ('''epidemiological week''') is used to report healthcare statistics, as with COVID-19 cases:<ref>{{cite journal |title=Norms and Standards in Epidemiology: Epidemiological Calendar 2000 |url=https://www3.paho.org/english/sha/be993calend.htm |issn=0256-1859 |journal=Epidemiological Bulletin |volume=20 |number=3 |date=September 1999 |access-date=2024-09-11 |publisher=[[Pan American Health Organization]]}}</ref>
<blockquote>The epidemiological week begins on Sunday and ends on Saturday. The first epidemiological week of the year ends on the first Saturday of January, provided that it falls at least four or more days into the month. Therefore, the first epidemiological week may actually begin in December of the previous year.</blockquote>

====Uses====
The [[semiconductor package#Date code|semiconductor package date code]] is often a 4 digit date code YYWW where the first two digits YY are the last 2 digits of the calendar year and the last two digits WW are the two-digit week number.<ref>{{cite web |publisher=Texas Instrument |url=http://focus.ti.com/quality/docs/gencontent.tsp?templateId=5909&navigationId=12626&contentId=153966 |title=Quality & Lead-free (Pb-free): Marking Convention |url-status=dead |archive-url=https://web.archive.org/web/20140405090712/http://focus.ti.com/quality/docs/gencontent.tsp?templateId=5909&navigationId=12626&contentId=153966 |archive-date=5 April 2014}}</ref><ref>{{cite web |publisher=Fairchild Semiconductor |url=http://www.fairchildsemi.com/support/packaging/topmark/dateCode4/ |title=Top Mark Convention – 4-Digit Date Code |url-status=dead |archive-url=https://web.archive.org/web/20140714111530/http://www.fairchildsemi.com/support/packaging/topmark/dateCode4/ |archive-date=14 July 2014}}</ref>

The [[tire code#DOT code|tire date code mandated by the US DOT]] is a 4 digit date code WWYY with two digits of the week number WW followed by the last two digits of the calendar year YY.<ref>{{cite web |url=https://www.law.cornell.edu/cfr/text/49/574.5 |title=49 CFR 574.5 – Tire identification requirements |website=Legal Information Institute}}</ref>