1.8 Date Calculator. Figure 1 diagrams the elements of the structure required to maintain the most essential information in a calendar date. Central to the designation of the date is the calendar system in use. Sometimes a calendar allows various formats for representing a date, e.g., “4 Mar 1943,” “March 4, 1943,” or even “3/4/43” and “4-3-43.” Which format is appropriate for interpreting the time period represented is indicated by the alias of the date. A standard time-keeping system for days is the Julian day number. The date string on the respective calendar is simply a signed integer value.