{S:X;X;0;0;An Everlasting Calendar{ITR-X}by Gerald L Fitton}
{S:X;X;0;1;Keywords:{ITT-X}Calendar Julian Gregorian Year Month Day Spreadsheet Fitton}
{S:X;X;0;2;Some History{ITR-X}{ITR-X}Before the year 46 BC all twelve months of the year except February had either 29 or 31 days. February always had 28. Most years had 355 days but, every so often the priests or politicians added an extra month in order to keep the seasons (particularly the Spring equinox) at or about the same time of the year every year. It was Julius Caesar who first tried to bring some regularity to the calendar. He ordered that the year 46 BC should have 445 days (to bring the Spring equinox close to the beginning of the Roman year ie in March) and that every year thereafter should have either 365 or 366 days. The extra day was to be added to the 29 days of February in every fourth year to make it a 30 day month. So you\æll see it was thanks to Julius Caesar that we have a variable length for February. He chose February because it was the last month of the year. The calendar was slightly modified by Augustus Caesar (who followed Julius Caesar). He renamed August after himself (otherwise we might have had a Sexember) and added an extra day to his month making August 31 days by reducing February to 28 days (except in leap years). Further, in an attempt to fine tune the Spring equinox, he decreed that the first leap year should be 8 AD so that 4 AD and earlier fourth years were not a leap years. His calendar for 8 AD was like that of any of our leap years today.}
{S:X;X;0;3;The Earth does not take exactly 365 days and 6 hours to go round the Sun. If it did then the Julian calendar would keep the seasons in synchronism with utter perfection. It takes about 11 minutes per year less than this. Over the centuries since 8 AD these eleven minutes per year added up so that, by the year 1582, the seasons had slipped by about ten days. Pope Gregory XIII was more concerned about Easter (which I think is on the first Sunday after the first full moon after the Spring equinox) and the other movable church festivals than about the farmers, and decreed that ten days should be dropped from the year 1582. The Roman Catholic countries adopted this Gregorian calendar almost immediately but Protestant countries were slower to accept it. In order to prevent a later problem with the accumulating 11 minutes Pope Gregory ordered that century years such as 1800, 1900 and 2100 should not be leap years unless, like the years 2000 and 2400, they were divisible by 400.}
{S:X;X;0;4;In Britain we continued to use the Julian calendar until 1752 by which time the \Éerror\æ amounted to eleven days. In Britain in the year 1752 the day after the 2nd September 1752 was the 14th September 1752. This unique September is produced by this spreadsheet. Some countries were even later than Britain in accepting the Gregorian calendar. Bulgaria adopted it in 1916 and the Soviet Union in 1918. The Greek Orthodox Church finally accepted it in 1924. So you can see that for the years 1582 to 1752 there was a discrepancy of 10 or 11 days between Britain and the Catholic countries. During that period this calendar spreadsheet is correct only for those countries that continued to use the Julian calendar. If you have the knowledge and expertise to modify this spreadsheet for another country then let me know and I'll include it on a future ZLine 4 disc.}
{S:X;X;0;5;How to use the spreadsheet{ITR-X}{ITR-X}Resultz saves the position of the \Éinput focus\æ with the document. This calendar spreadsheet has been saved with the input focus in slot n2. If the input focus is not in that slot then use the mouse to position it in the slot n2. This contains the year as 1994. Type in another year, for example 1066, and tap <Return>. There will be a short delay whilst the spreadsheet recalculates. The Battle of Hastings was on the 14th October 1066 and you will see that it was a Saturday. My History teacher had a theory that all wars broke out at 3.00 pm on Sunday afternoons when everyone had just got out of the pub! We went to war with Germany on the 3rdáSeptemberá1939. I can\æt remember when Pearl Harbour was attacked by the Japanese but I seem to remember that was a Sunday afternoon, possibly the 7tháDecemberá1941 at about 3.00 pm. The Spanish Armada was on Friday the 19tháJulyá1588. My History teacher would have loved to find out what day of the week the Bastille was stormed and there may be some who want to know what day of the week the original StáSwithan\æs day was on. Contributions to this discussion will be welcome, particularly if you know the date of some important events.}
{S:X;X;0;6;How it works{ITR-X}{ITR-X}Slot w6 contains a key formula that returns the day of the week (numbers 0 to 6 representing Sunday to Saturday respectively) for the 1st January of the year in slot n2. Actually it\æs two slightly different formulae, one for the years before 1752 and one for the years after 1752\\\; an \Éif\æ is used to decide which formula is used. The formula uses the year entered into n2 as input and calculates the number of days between a fixed date (eg 1st January in the year 1áAD) and the year chosen (in slot n2) by counting 365 days per year plus an extra day for every leap year. This number of days is divided by 7 and the remainder used to decide on what day of the week the 1st January fell for our chosen (n2) year. In slot x6 the date for the first Sunday in January is calculated (using w6 as input). A number between 2 and 8 (inclusive) is returned. The formula in v7 for the number of days in February looks complicated but all it does is to work out whether the year is a leap year or not and returns either 28 or 29 appropriately.}
{S:X;X;0;7;In the x column the date of the first Sunday of each month is returned for all twelve months. It is the values in this column which form the input to the visible part of the calendar. I don't know why exactly, but, until I added in a 0.5 before using the function int (integer), I occasionally got wrong values.}
{S:X;X;0;8;Slot c9 contains the date of the first Sunday in January taken from x6. By a process of adding 7s (eg slot d9 contains c9+7) the remaining Sunday dates in January can be found. An \Éif\æ is used in the first week of the month to avoid negative dates and, at the end of the month, another \Éif\æ is used to prevent values greater than the number of days in the month appearing. September is treated differently from the other months. The year is tested to see if it is 1752. If not then the standard formula is used, if the year is 1752 then the special 1752 values are entered. Slot v14 (which contains the number of days in September) also has an \Éif\æ which tests whether n2 (the year) is 1752 or not.}
{S:X;X;0;9;I have to confess I made a bit of a mess of choosing the best way of replicating each month so I have got rid of all the $ signs (which fix the replication) in order to hide my embarrassment. I got rid of the $s by using search and replace to replace the $ signs with nothing. So now you can\æt see what a mess I made of my choice of where to put the $s!}
{S:X;X;0;10;Slot h5 contains a hidden error message triggered by an \Éif\æ if you enter a year before 5 AD.}
{S:X;X;0;11;Customising{ITR-X}{ITR-X}You can insert rows and columns with impunity. All the slot references change automatically. Be careful about deleting rows, parts of rows or columns. Don\æt use the master copy! You can add your own graphics etc and print calendars for all your friends. Finally you can use \ÉSnapshot\æ using the Editá-áMake - Makeáconstant menu and then delete columns t to y) to make a simple calendar for a chosen year that can be customised without fear of damaging any formula.}
{S:X;X;0;12;Printing{ITR-X}{ITR-X}Some people do have problems printing this calendar. I could have taken the easy way out and completely hidden columns t to z by making them zero width. Then nobody would have printing problems but they may not have been able to open up the columns again! Anyway here is what I have done and how to fix it if the printing does go awry for you.}
{S:X;X;0;13;I have arranged for the columns t to z containing the \Éhidden\æ calculations to appear on the second page (ie on page xá=á2) so, what you have to do is to print only the first page where both x and y are 1.}
{S:X;X;0;14;I prefer to print out using Outline fonts rather than the CharPrint printer drivers. I have used 10 point Homerton. I suggest that you use a sans serif font such as Acorn\æs Homerton.Medium (Helvetica) or Beebug\æs Vogue (Avant Guarde) rather than one of the serifed fonts such as Trinity.Medium (Times) or Paladin.Roman (Palatino). By the way you can get some interesting effects with decorative fonts such as EFF\æs Hot Dog or Horror!}
