GNU Emacs Calc 2.02 Manual
8.5 Date Arithmetic
The commands described in this section perform various conversions
and calculations involving date forms (see section 5.9 Date Forms). They
use the t (for time/date) prefix key followed by shifted
letters.
The simplest date arithmetic is done using the regular + and -
commands. In particular, adding a number to a date form advances the
date form by a certain number of days; adding an HMS form to a date
form advances the date by a certain amount of time; and subtracting two
date forms produces a difference measured in days. The commands
described here provide additional, more specialized operations on dates.
Many of these commands accept a numeric prefix argument; if you give
plain C-u as the prefix, these commands will instead take the
additional argument from the top of the stack.
