31.3 Counting Days
M-=
Display the number of days in the current region
( calendar-count-days-region).
To determine the number of days in a range, set the mark on one
date using C-SPC, move point to another date, and type M-=
( calendar-count-days-region). The numbers of days shown is
inclusive; that is, it includes the days specified by mark and
point.