At the start you select the calendar of which you know the date by highlighting it with the cursor and pressing <ENTER>. You can then enter first the day, press <ENTER>, highlight the month using the cursor again, press <ENTER> and finally enter the year, followed by <ENTER>. Now you will be switched to the right side where you highlight the calendar which you want to know, press <ENTER> and presto: You have your date (including the day of the week).
Historians often need only to know the equivalent month(s) or only the equivalent year(s) of a given month or year respectively. Instead of two awkward operations by consecutively entering the first and the last day in order to obtain the range required you simply press <ENTER> at the day-menu (without entering a day) or/and at the month (*w/o month* is always the first choice in the month-menu) and you get the equivalent in months or years on the right side.
Implausible input of dates is checked and the program gives you a short message why your input did not make any sense, e.g. entering Sivish-years into the Mali (Turkish Financial) calendar. Error checking also works on the output side, e.g. Christian dates before 622 AD cannot be converted into Islamic dates as no <BEFORE-HIJRA>- chronology exists.
Special input rules work for the French Revolution Era (Roman numbers -small or caps - for the years because only those have been used in historical documents) and for the Jalali- and Yezdegerd-eras when days were not numbered but identified by name. In order not to confuse you with the need to spell correctly the name of a given day the menu opens in these cases with prefigured day captions.
The program also ckecks if the date input confirms to the rules governing Epagomena (in the Coptic and Armenian calendars) or Ve-Adar in the Jewish calendar and it does not accept 29 February in normal years, or similar nonsense.
After getting your conversion you could press <ENTER> to make one more conversion or <ESCAPE> to quit.
Some very basic comments to the individual calendars (a
thorough explanation would need a book!):
--1. The Christian calendar as in the first menu item is
based on Julian dates until the Gregorian calendar
reform and later on the reformed dates. In case you need
Julian dates even for a period after the reform a separate
purely Julian menu item is included at the end of the list.
Always bear in mind though that the Gregorian reform was
applied from its start only in Catholic states and only
later elsewhere (e.g. in England in the 18th century).
Still more confusion can arise from different New Year
dates, e.g. in some countries the new year would begin on
December 25, resulting in different years for dates of the
same month of December!
The division between BC- and AD-dates runs between 1 BC and
1 AD; historiography does not know a year 0!
--2. The Islamic Lunar Calendar is based on the schematic
rules applied in historiography (e.g. Encyclopaedia of
Islam, Wuestenfeld tables etc.) with two options on the
output side : Era beginning 16 July 622 (most accepted
date) or 15 July 622. The difference is NOT consistently
one day only (there would not have been any need for two
options then) as according to the sources consulted the
exact sequence of intercalary Islamic years depends on the
choice of the era (first day). Anyhow, everybody aware a
bit of the problems of the Islamic Lunar calendar knows
that a conversion based on arithmetic or even on astronomic
data has a margin of error of one day (possibly even more).
(Reasons: Actual sighting of the moon in different regions
by different people; overlapping of days due to the
beginning of the new Islamic day at sunset vs. midnight in
modern chronology).
Therefore, the day of the week is always given as a
convenient method of control.
--3. The Islamic Solar Calendar (ruled other than the lunar
calendar by purely astronomical criteria conforming to the
traditional Shiite preference for calendar calculation
based on astronomical data) as used in Iran is relatively
new (albeit based on the Hijra-date) as until the end of
the Qajar-dynasty other calendars were in use beside the
Lunar calendar; so dates until 1304 After Hijra in solar
years are rejected.
--4. The Jalali-calendar rules have never been without some
dispute. I follow Taqizadeh's findings in choosing the most
probable solution.
--5. The Turkish financial calendar (also known as the
Mali- or Rumi-calendar) was in use in the Ottoman empire
during its later period, mostly along with the lunar Hijra-
calendar. It has rather peculiar rules for aligning the
numbering of (longer) solar with (shorter) lunar years by
regularly dropping entire years (Sivish-years) apart from
other peculiarities and errors were therefore inevitable. Although the Computus-program applies correct conversion
rules it is, therefore, wise to counterckeck by comparing
the Mali-dates with the often similtaneously given Lunar
calendar dates taking into account the day of the week.
--6. The Armenians know so-called lesser and greater eras;
I applied the greater era which for historiography
seems to be the more commonly applied calendar.
--7. The Jewish calendar (era: creation of the world) has
only been in use since the Middle Ages; nevertheless
any earlier date input is accepted (I could simply not
resist giving Christian BC-equivalents to dates going back
to the creation of the world according to Jewish belief!).
--8. To know the date of Easter-Sunday it is only needed to
enter the year. The result is computed according to the
different methods applied before and after the Gregorian
calendar reform.
Dr. Gerhard Behrens
Munich/Germany
Download computus.zip here (28,999)