Definition of Week Numbers

Week numbers are useful for scheduling and planning. ISO 8601 defines a week as beginning on a Monday (Day 1) and ending on a Sunday (Day 7). A year can have 52 or 53 weeks. Week 1 of the year is defined as the week containing the 4th January or equivalent definitions such as the week containing the first Thursday of the year. The complication is that the 1st/2nd/3rd January can fall in Week 52 (or 53) of the prior year and the 29th/30th/31st December can be in Week 1 of the following year.

The Week Number displayed in the date block at the upper right of the home page is calculated per ISO 8601. I used the week containing 4th January as the basis for a Javascript function which takes a date as an argument, calculates the corresponding Week Number and returns a string in the form "Week ww of yyyy".