$month(calendar) returns the start of the current month according to the given calendar.
For example, if server date is 05-JAN-2005, and the current month in the Fiscal calendar is from 03-JAN-2005 to 06-FEB-2005, then the following expression will return 01/03/2005 (the beginning of the current month according to the Fiscal calendar):
$month(Fiscal)