The commands described in this section perform various conversions and calculations involving date forms (see 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.