[unwind]

Week numbers are a very common way of talking about time in some locales.

For instance in my native Sweden, it's very common when e.g. scheduling things at work to talk about which week something will happen.

Sites like http://vecka.nu make it easy to check the current week number (the domain name translates as "week.now") whenever you have internet access, paper calendars include it, and so on. It's really very common.