Week number in the USA
The US system has weeks from Sunday through
Saturday, and partial weeks at the beginning and the end of the year.
The first week of a year is the week that contains january 1.
Week number in Europe
The ISO week date system is being used in Europe and some Asian countrys.
It has weeks from Monday to Sunday. The first week of a year is the week
that contains the first Thursday of a year.
See also: Time zones