ISO 8601 Week Number
If you select the corresponding item on the Settings Dialog, Titlebar Date-Time will display the ISO 8601 week number. The first day of an ISO week is Monday, and week one for the year is the week that contains the first Thursday of the year. If your country doesn't use ISO week numbers, you can modify the week number on the Advanced Settings Dialog.
For information on which countries use a value that differs from the ISO week number, see http://www.pjh2.de/datetime/weeknumber/wnd.php.
Go to the Titlebar Date-Time home page or the download page.