(1) Two forms of the application---"InterCal" and "InterCalFP"---see below for which to use. For performance reasons, some users may wish to stick with InterCal 1.3, which is still available via ftp. See "Selection of the Correct Version" below for more information.
(2) Chinese Calendar
(3) French Revolutionary Calendar rules corrected
(4) InterCal now remembers last-used Primary and Secondary Calendar Systems and comes up with them in force
(5) Default Mayan/Gregorian correlation date changed to 584283 (was 584285)
(6) The explanatory documents ("Calendar System Facts" and "InterCal User's Guide") are now distributed as Acrobat™ PDF files. Please use Acrobat™ Reader 3 or later to view the files. Acrobat™ Reader is available at no charge from a variety of sources, including any Info-Mac mirror site or http://www.adobe.com.
Introduction
This is the fourth public release of InterCal, a freeware date conversion, calendar comparison, and holiday calculation program. It is not a daily appointment calendar. It displays calendars, one month at a time, for any month of any year in any of several calendar systems. For each day in the displayed month of the Primary system, corresponding dates in another calendar system (the Secondary system) can be shown. Any implemented system can be chosen as either Primary or Secondary. For any selected single day, the corresponding dates in all implemented calendar systems can appear in a separate window.
Calendar systems implemented are: Gregorian, Julian, "Western Historical" (a hybrid of the Julian and Gregorian), Jewish, Islamic, Mayan, Chinese, French Revolutionary, and the Elliott Super (invented by the author of InterCal).
Certain religious holydays and festivals are highlighted (under user control) when they occur in a displayed month, regardless of which calendrical system is in use at the time. Some which can be highlighted are Easter, Rosh Hashonah, Hanukah, ‘Id al-Fitr, and the first day of Ramadan.
Limitations
InterCal exists in a 680x0-native version only, and must run on PowerPC's in emulation mode. I am very sorry that there is no native Power PC version and am anxious to remedy the situation. However, I will need to get a new development environment and port InterCal to it—that will take some money and lots of time. Actually, until version 1.4 and the Chinese calendar, performance was never an issue. But now it is very important.
InterCal was designed with 16-inch or larger monitors in mind. But smaller monitors can be used if one is willing to scroll around the display.
InterCal requires System 6 or later and 32-bit QuickDraw.
InterCal was developed and tested on a Mac IIci running System 7.6. It has been run and casually tested on several other machines (MacPlus, PowerBook, Centris, Performa, PowerMac) running System 6.0.5, various versions of System 7, and Mac OS 8.
Printing has been tested on an NEC Silentwriter™ Model 95 laser printer using both LaserWriter 7, LaserWriter 8, and Adobe™ drivers. It has also been tested on an HP PaintJet™ using the driver provided by HP. It has never been tested on a QuickDraw printer (such as the ImageWriter™).
Acknowledgements
InterCal was developed using Symantec's C++ Version 7.0, Symantec's Visual Architect™, and the Think Class Library. Using those tools shortened development time considerably, but led to an unexpectedly large size for the program. It requires 1000K to run.
The InterCal icon was designed and drawn by my daughter Nicole when she was 13.
As described in more detail in "Calendar System Facts", my ability to include the Jewish calendar in Version 1.0 depended on access to the source code to a freeware program called "Jewish Calendar" written by Frank Yellin. It is a very nice program and treats the Jewish calendar in more depth than InterCal.
A few months before the release of InterCal 1.4, a wonderful book appeared which contains the rules for a wide variety of calendars. It is called Calendrical Calculations by Dershowitz and Reingold. I strongly recommend it to anyone interested in calendars of the world. I have used it as my "bible" to determine the rules of all calendars implemented or modified in InterCal in version 1.4 or later.
The rules for the French Revolutionary calendar were originally given to me by Dave Stewart, Assistant Professor of History at Hillsdale College. The rules in Calendrical Calculations differ from those given by Stewart. InterCal1.4 switched to the rules from the book. Thanks to Ed Reingold for providing me with sample Lisp code illustrating the key algorithms.
The list of Mayan Correlations and their values comes from the freeware program MacMaya by Steve Stearns.
Changes to the format of the Holidays dialog box beginning with Version 1.2 are based on suggestions by Walter Ian Kaye. My apologies to him for not adding the Bahá’í calendar yet—I promise it for the very next version.
Package Contents (Folder containing five items)
(1)—This ReadMe file, which was written using SimpleText, not TeachText, and so has some text styling which will not be visible if viewed using TeachText.
(2)—A User's Guide (included for completeness—InterCal is a simple program with very few commands and should be easy to figure out without a manual)—distributed as a PDF.
(3)—A document entitled "Calendar System Facts" which contains a general discussion of calendars and detailed descriptions of each implemented calendar—also in PDF format.
(4 & 5)—Two forms of Version 1.4 of the InterCal application. Be sure to use the one correct for your machine as explained below.
Selection of the Correct Version of the Application To Use
Two applications have been distributed. One is called "InterCalFP"; the other is called just plain "InterCal". Both programs have identical functionality and appearance. They differ only in how they implement floating point calculations. "InterCalFP" can only be used on certain machines, but has much better performance on those machines. The separate versions became necessary with the introduction of the Chinese calendar, because it uses apparent positions of the real sun and moon. Calculating those positions requires large numbers of floating-point operations.
"InterCalFP" is recommended for use on all 68040 machines. It is also recommended for 68020 and 68030 machines if the optional floating-point co-processor chip, 68881 or 68882, has been installed. InterCalFP will hang your system if it does not have one of the recommended configurations. Even with the use of the special hardware, InterCalFP can be annoyingly slow. Calculation of the tables needed to specify a single year in the Chinese calendar takes 3 or 4 seconds on a 68030 with a 68882 installed.
The other executable, "InterCal", will run on any Macintosh. However, its performance is tolerable only on PowerPC's. It uses only instructions recognized by the 68000 (which are emulated on PowerPC's). On a PowerPC "InterCal"'s performance is also a little slow—about 3 seconds per Chinese year calculated. On a 68030 machine without the 68881 or 68882, "InterCal" takes about 90 seconds for the same task!
If users are not interested in the Chinese or French Revolutionary calendars, they can stick with Version 1.3, whose performance is excellent. Time and finances permitting, work will begin within a few months on a PowerPC-native version.
Version 1.3 is available via anonymous ftp at the following site:
alumni.caltech.edu
in directory pub/denis
Please note that the 3-4 second delays (or longer on very old Macs) described above only occur when a Chinese date is needed and the Chinese year it is in is not already in InterCal's internal cache. Once the initial display is up (this invariably involves the calculation of one Chinese date, and so an initial delay is inevitable), most users of InterCal will be able to use the program with no further performance problems. Chinese dates are needed under the following circumstances only: (1) the Primary calendar is Chinese and the date controls are used to enter a different year; (2) the Secondary calendar is Chinese and the date controls are used to cross a Chinese Year boundary; (3) regardless of Primary and Secondary system settings, the "selected" date (see user's guide) is changed to a date in a different Chinese year from the previously selected date. If the user does not select dates, and if the user never chooses Chinese for Primary or Secondary system, the performance of InterCal 1.4 is excellent.
No one may distribute InterCal for profit in any form, including (but not limited to) electronic information service distribution, bulletin board distribution, and magnetic or optical medium distribution. Non-profit distribution of the software is fine, providing that the software is not modified in any way, and the complete works and documentation of the software are included in the distribution package.
Disclaimer
The formulas used in the various calendars and the statements concerning calendars made in "Calendar System Facts" are true to the best of my knowledge. However, their accuracy is not guaranteed.
Version History
Version 1.3—
Added support for the Mayan Calendar.
Fixed a bug with the Jewish calendar which, under certain special circumstances, caused incorrect displays in both the main and date windows between 1 Cheshvan and 29 Elul in the year 1 B.W.
Fixed a bug which sometimes caused incorrect secondary calendar dates to be displayed if the primary calendar system was Western Historical and the displayed month was October 1582.
Version 1.2—
Added the printing capability;
Changed the appearance and behavior of the Holidays dialog box;
Added Julian Easter and Julian Pentecost to the implemented holidays.
Fixed a bug which sometimes caused an invalid Jewish calendar display—the symptom was months with the wrong number of days, occasionally causing holidays to be displayed in the wrong month.
Added a workaround for the problem (discussed in the Known Problems section of the Users' Guide) of truncated popup month and era menus. The frequency of the appearance of the problem was reduced for System 7, but the problem still occurs and a different menu display problem appeared in OS 8.
Version 1.1— (Never publicly released)
Added the French Revolutionary calendar.
Version 1.0—
Initial release. Support for Gregorian, Julian, "Western Historical", Jewish, Islamic, and Elliott Super calendars.
My e-mail address
Comments, corrections, bug reports, and suggestions are welcome via e-mail to the following address:
