To help correct the drift of manmade calendars away from cycles, mundane and celestial, time-keeping systems have adopted a series of complex intercalary or epagomenal units of time to compensate. In ancient times—and yet today for countries like India and China that maintain lunisolar timetables, there were leap months added to the year to keep observances in their seasons. The year cannot be divided equally among our measures in any case, but cherishing regularity and symmetry, the Romans (with many inheritors) counted three-hundred sixty days to the year, with some uncountable days.
In the Chinese tradition, the extra month went unnamed, but in Rome there is evidence that this thirteenth month Undecimber (really eleven or rather December plus one, as originally the fifty-seven dreary days of Winter were not considered worthy of reckoning (lousy Smarch weather) until the reforms of King Numa, where the months included at the beginning of the year were named after gods or rituals to make a twelve or thirteen month annual cycle. The Gregorian calendar mostly eliminated the need for inserting a whole month to realign the date and by many schedules there is only the one embolismic day in February, once every four years—with restrictions, ninety-seven in the span of four-hundred years. However, in the West at least and with the bankers’ hours it shares with the rest of the commercial world, there is one other formal, larger unit of time that can straddle (or just fall short of) the conventional year: the International Office of Standards (ISO) counts a the first Thursday of the year as the first week of the year—sort of an overlay for the daily calendar and this is parsed into three-hundred sixty-four or three-hundred seventy-one days—to speak in terms of full work-weeks to a year for payroll purposes and financial records. The Roman system was contrived originally of course to keep important commemorations (and practices) from sliding away but the tweaks were also instituted to ensure that taxes and tribute could be collected in a timely manner, which due on the first day of the month, named Kalends (Latin for “those called” and derived from the name for the ledgers of accountants, kalendaria).
