ISO 8601 Calendar
The week numbering was reintroduced by ISO in June 1988 to solve the problem that each week in a year should have seven days even for the first and last week of the year.
Let’s suppose that a week is overlapping between two years then Thursday of this week decides whether it is an ISO week 53 of the previous year or the ISO week 1 of the next year.
If Thursday of the over-lapping week falls on or before 31st Dec then that whole week will be considered as ISO week 52/53 of the previous year or if Thursday falls on or after 1st Jan then it will be considered as ISO week1 of the next year.
Gregorian Calendar
In Gregorian Calendar Week numbering always starts from the 1st day of the year and the first and last week of the year doesn’t need to have 7 days. Let’s suppose that 1st Jan of a year is Saturday then, in that case, the first week will have only 2 days and same with the previous year that it will have only 5 days in the last week.
How to select your preferred Calendar type in Tableau?
