Annual calendar years. An annual timepiece calendar is less complicated and expensive than a perpetual timepiece calendar, which will not require manual adjustment till 2100. That year will not be a leap year, even though its number is evenly divisible by 4. Ancient calendars (static) may always have been annual, even after the length of the calendar year was fixed at (avg.) 365.25 days by the Julian Calendar (46 BC). Early Romans observed an 8-day market week, called the nundinal cycle, until the seven-day week was adopted during the reign of Emperor Constantine the Great (306-337). A goal of modern calendar reform
365-day calendar 365-day calendar A 365-day calendar consists of exactly 365 days per year (no leap days), and is primarily used in computer models and as an assumption in every-day calculations. For example, a calculation of a daily rate may use an annual total divided by exactly 365. Interest rates in some banks are calculated using a 365-day calendar. Some Mesoamerican calendars used a 365-day year with no leap year, resulting in a gradual shift of the seasons relative to the calendar. This includes the Maya Haab' and the Aztec Xiuhpohualli calendars. Some versions of the Zoroastrian calendar also use a fixed