Terms related to the Maya calendar are described in the About the Maya Calendar section.
The date conversions are all menu items in the Find menu.
Chac can convert a calendar date, Long Count, Tzolk'in, Haab', Calendar Round, Julian day number or Proleptic Gregorian Calendar into a Maya calendar date. It can also find dates using distance numbers or Long Reckonings and draw an inscription if the resulting date is within the range of 0 - 19 Bak'tuns. It can find the next or last heliacal rising or setting or cosmical rising or setting of Venus, the next or last lunar or solar eclipse, Solstices and Equinoxes and Zenith Passage Days and draw an inscription if the result is in range. Each of these conversions is done using a panel. Chac can find the next or last seating of 819 day count with the sub-menus of the 819 day count menu item. Chac can find today's date in the Maya calendar using the Find -> Today menu item. When the application is launched without using a saved inscription, a new inscription is opened with today's date.
Starting with Chac 2.0.3 The panels and menu items are smarter than they were in earlier versions. The Today menu item will be disabled if the front inscription is today's date. The OK button will be disabled if the date in a panel is the same as the date in the front inscription or you have selected an illegal parameter in a panel. This is particularly noticeable in the Find > Date... panel. The OK button will only be enabled if you have a valid year in the year field. This means only digits or minus sign digits for the year, no year zero with a historical dating suffix, no negative year with a historical dating suffix and no year negative zero. The historical dating suffixes accepted are "BC", "BCE", "B.C.", "B.C.E.", "AD", "A.D.", "CE" and "C.E." with no other text other than spaces. Only one historical dating suffix will be accepted. The OK button will be disabled if the year text field is blank. If a panel's OK button is disabled, check the following:
1. One of the pop up menu items is disabled. This means that an illegal parameter is selected.
2. The date in the panel is the same as the front inscription.
3. An illegal year string is in the year field in the date panel.
4. The day of the month in the day menu is greater that the number of days in the month. See the rules about leap year in Gregorian leap centuries.
In the distance numbers panel the button will only be tilted "set inscription" if the resulting inscription is within the range of Long Count 13.0.0.0.0 - 19.19.19.17.19. If not the button will have a title of "out of range" and be disabled and unhighlighted. If the date on the distance panel is the same as the front inscription it will still be entitled "set inscription" but the button will be disabled and unhighlighted. Any time you change any user editable item in the distance panel it will automatically re-calculate and display the result so the distance panel has no OK button.
In the Long Reckonings panel the button will only be tilted "set inscription" if the resulting inscription is within the range of Long Count 13.0.0.0.0 - 19.19.19.17.19. If not the button will have a title of "out of range" and be disabled and unhighlighted. If the date on the distance panel is the same as the front inscription it will still be entitled "set inscription" but the button will be disabled and unhighlighted. If the ring number plus the distance number is out-of-range (not in the current creation) error will be displayed in the date field. Any time you change any user editable item in the distance panel it will automatically re-calculate and display the result so the distance panel has no OK button.
This is also true of the Julian day number panel. If the number string in the text field can't be converted to a real number by sending a doubleValue message to the Cocoa NSTextString in the text field, the OK button will be disabled. Since the Julian day starts at noon, the real number returned by the doubleValue message will be rounded to an integer. If the integer is the same as the Julian day number of the front inscription the OK button will be disabled.
The proleptic Gregorian calendar, Venus Cycle, Eclipse, Solstices and Equinoxes and Zenith Passage Days panels are similar. If there is an invalid date entry or if the date is out of range, the error will be described in a text field below the data controls and the Set Inscription button will be disabled.
Implementing smart menus and panels is complex and difficult to program and test. If you're sure one of these is buggy, E-mail me and I'll fix it.
The Chac > Preferences... menu item will display a panel that you can use to set the following options for displaying a Maya calendar inscription:
correlation constant
dating of negative years
head variant or symbolic Long Count glyphs
new moon system
moon number
year Bearer system
819 day count
When you change the preferences it will only change them in the front inscription if one is open and in subsequent inscriptions. The preferences you choose will be saved when you quit the program. Other inscriptions won't be changed, either ones open but not in front or saved in files. Each inscription's preferences are part of the object that encapsulates its data. This is so you can view multiple inscriptions with different options. For example you might want to display the same date with the Long Count as head glyphs in one window and symbolic glyphs in another or you might want to compare the same date with two different correlation constants. The small text field in the lower left part of an inscription lists the options used to display it.
You can use the File > Save... menu item to save a date as an inscription document (file type 'insc') which has an icon like this: