http://www.perlmonks.org?node_id=489713


in reply to Re^2: ISO Date Week Number
in thread ISO Date Week Number

Yes, it corresponds to ISO's standard definition of a week number.

Tested on:
Linux 2.4.21, Perl v5.6.1
Linux 2.6.10, Perl v5.8.3
Mac OS X Tiger 10.4.2, Perl v5.8.6

Of course, if the OP is still using v5.0 I've got no idea what kind of old OS they're using, so YMMV.