Talk:Perpetual calendar

Removed Redirection
Old Redirection: Talk:International_Fixed_Calendar

I have removed the redirection from this talk page because I believe it to only be tangentially and not directly related to this topic. --Stux 21:50, 22 October 2005 (UTC)

Example Perpetual Calendar
I think this entry should have an example of the gregorian calendar or even formulas themselves. At the very least links to online perpetual calendars would be useful. I found one here by searching Google but I don't know if its a good example to link. If it had days of the week explictly listed, it would be more useful. --Stux 21:50, 22 October 2005 (UTC)

Example Perpetual Calendar
Here's an example I just put up:   --User:KarenSDR

Perpetual Calendar Formula
I added an example of a formula that can be used to create a perpetual calendar. I added some links to my web site and then discovered that I did not use the formula in the javascript. I then removed the links. Denmarks 21:21, 12 February 2006 (UTC)

I added a second formula. Denmarks 22:07, 12 February 2006 (UTC)

The second Zeller formula is completely wrong try it for September 1 1939 or March 1 2007...

Interesting webpage about different types of Christian Zeller algorythms one can find here:

http://www.merlyn.demon.co.uk/zeller-c.htm

Cheers,

Polimerek 01:41, 27 February 2006 (UTC)

Perpetual calendar in watches?
I'd like to see some information on how mechanical watches implement perpetual calendars. 218.215.32.173 16:27, 6 January 2007 (UTC)

Could anyone…
…translate the content from ru:Вечный календарь? — 87.236.197.182 08:23, 22 February 2007 (UTC)

Fun little fact: Weekdays run on cycles of 6,5,6,11,6,5,6,11...ect. A total 4 times in a cycle of 28 years. In other words, if you have a day such as March 5th fall on a Monday in a particular year, that day of the week will fall either 5,6, or 11 years later depending on the cycle. Try and find the cycle of you birth dates and see what cycle you are in.

Perpetual calendar and Easter (and Friday the 13th)
It is very easy to combine things like those. See for instance a program simply called "Calendar" written in 1993 that does those things and more. It will give the correct day of the week since the start of the Gregorian Calendar (October 15, 1582) until the year 9999. That year was not chosen as the year the algorithm would break by the author, but only to put some arbitrary limit of 4 digits for a year. The program does other calendar-related calculations as well: 97.103.81.29 (talk) 00:27, 28 October 2008 (UTC)

Required math skills & Reading Level too High
After literally years of frustration trying to do date math in spreadsheets, I'm collecting all the date calculations I can find/create into one spreadsheet and publishing it. I came here in search of a single fundamental algorithm. This may be it but, after reading it several times. it's still not clear how this works.

Thank you for writing this article. It really sounds like whoever contributed knew what they were talking about. I want to rewrite it so the average person could understand it. How can we make it so it's less dense. It's written by someone who understands the subject matter for others who understand the subject matter. It needs to be stepped down to a level below that of a professional so students can get it too.

--PB-- Netscr1be (talk) 15:08, 3 January 2011 (UTC)

Algorithm for a Perpetual calendar
Dear Mr.Netscr1be, my english is not good, sorry. Please see by http://commons.wikimedia.org/wiki/Category:Perpetual_calendars the file "Permanent_Calendar" and http://commons.wikimedia.org/wiki/Wikitable_calendar. Here is a simple solution. The result is very easy to control. The algorithm is: The days of the week for January and February are the first line in the second from February through December. I wish you much fun. greetings from saxony Karl Nimtsch --LenderCarl (talk) 13:22, 7 February 2011 (UTC)

source: The first print was by C.H.Beck-Munic 1992 "Juristenkalender/Steuerberaterkalender". The next print by "Max-Planck-Institut" Heidelberg, see by "Sterne und Weltraum" 5/93. The next print was a poster in special nr.5 from march in year 2000 by "Sterne und Weltraum". I am the dokument for "the first perpedual and permanent calendar" from "Guinnessbuch-Verlag" oct/1998 --LenderCarl (talk) 10:13, 12 February 2011 (UTC)

Perpetual Julian and Gregorian calendar table
I've been trying to improve this table, but "92.234.23.201" keeps making up different excuses to undo all my work at once. Here's the latest: "(You have removed the explanation of how to convert from Julian to Gregorian and vice versa for no apparent reason. You don't need two columns of Julian centuries as the Julian calendar repeats every 700 years.)" I removed the explanation of how to convert from the section on the Perpetual Calendar Table because it doesn't belong there. This is an article on Perpetual Calendars, not "How to convert between Julian and Gregorian dates". Including the conversion confuses the instruction on how to actually use the table. Below the table, the example was muddled, confused, and incorrect. I've replaced it with one that makes it absolutely clear how to use the Table. I am trying to produce a table that is compact enough that someone can print it out and put it in a wallet, but still be understandable; anything more complicated than that defeats the purpose of a Perpetual Calendar Table. So I shortened the month names to the 3-character unambiguous abbreviations commonly used, and shortened the DoW names to Su/M/Tu/W/Th/F/Sa, the shortest unambiguous abbreviations, which are commonly used in compact calendars. I INSERTED the blank spaces in the Remaining Digits columns to make it easier to follow the progression from year to year (it's annoying to find a larger number to the left of a smaller number on a different line) and consolidated them into 4 groups showing the 28-year cycles. The reason for two columns of Julian centuries was to illustrate the very fact that it DOES repeat every 700 years. The mathematics of this are not obvious to everyone, as some of the other comments here indicate. There were THREE columns of Gregorian centuries, and 92.234.23.201 hasn't said a single word about that. I've added the r0-r6 indicators to show how these table rows have in common that remainder when divided by 7. Without two examples on each row, it may not be obvious that's what's being shown, but I'll give this a shot to see if it'll make you happy so we can avoid a revert war (a pretty one-sided one, as I keep making changes to address 92.234.23.201's objections, and 92.234.23.201 reverts all the work I've done, including other things you haven't objected to). Julian and Gregorian dates are now given nearly identical treatment in the table, with only one more cycle of Gregorian hundreds to make up for the fact that the skipped values may make it a bit more difficult to follow their pattern. The Monster (talk) 00:11, 13 September 2011 (UTC)
 * If you want a perpetual calendar to go in a wallet you can print it out to any desired resolution from File:Perpetual Calendar (1753-2180).png. 92.234.23.201 (talk) 12:06, 13 September 2011 (UTC)
 * That's a ridiculous suggestion. That file is way too complicated compared to this:

I've gone to a lot of work to make these improvements, and you keep reverting EVERYTHING to an older version that incorporates none of the improvements, including those to which you've expressed no objection. Stop it. I will now treat these reversions by a non-logged-in user as vandalism, unless and until a consensus is reached to the contrary. The Monster (talk) 13:45, 13 September 2011 (UTC)
 * Let me spell it out.  In Wikipedia we work by consensus.  You may think the changes are improvements, but then they're your changes.   I've agreed to the arrangement of the tens and units of the year.   I haven't agreed to r÷7, r÷4, DOW, Sep, #, or any other nonsense.   Nor has anybody else.   I don't agree that you should inform readers that 3 February 4567 will be a Tuesday when anyone who knows anything about the subject knows that it won't be.   If you can get other editors to  agree with  your way of thinking, fine, but otherwise leave the article alone.   The wallet calendar has already been done - see the third external link at the bottom of the page. 92.234.23.201 (talk) 17:02, 13 September 2011 (UTC)
 * You sure don't look like you're trying to reach a consensus. You are the only person reverting my changes, which doesn't seem like a "consensus" to me at all.  Your stated reason for opposing the 2/3/4567 example (that by then we'll have modified the rules yet again from the Gregorian reckoning) is completely bogus for a PERPETUAL calendar, and hardly an excuse to replace it with the 6/6/6666 example, a date by which it's even more likely that changes will be made, and an example that does not even correctly answer the question of what day of the week that date is.  It's one thing to hate "Sep" for September etc.; that's a style question.  It's another to defend something that is factually incorrect. 6/6/6666 Gregorian is a Wednesday, but you keep reverting to an example that says it's a Tuesday.  Stop it. There can't be a "consensus" that trumps fact. The Monster (talk) 01:37, 14 September 2011 (UTC)
 * Now The Monster is saying that calendars must have the same rules perpetually - I don't know one system for which this claim is true.  (S)he says it's fact that 6 June 6666 will be a Wednesday - is (s)he a time traveller from the distant future? 92.234.23.201 (talk) 13:27, 14 September 2011 (UTC)
 * When the rules were changed, the name "Julian" changed to "Gregorian". The section in question provides a perpetual calendar table for both of these rule sets. The rules for the Gregorian calendar make 6/6/6666 a Wednesday, not a Tuesday.  That is a fact.  Although many proposals have been made to modify those rules to address error expected to accumulate in a few millenia, no such rules have been adopted.  If I'm a "time traveler" for asserting that the rules that exist today make 6/6/6666 a Wednesday, then what are you for changing the example to say it is a Tuesday?  You have cited no authority to support the example to which you keep reverting.  I have confirmed the accuracy of my example in both Microsoft Excel and OpenOffice Calc., as well as checking other perpetual calendars, such as the "10,000-year Calendar". Your continued reversions to an inaccurate example are indefensible.The Monster (talk) 14:01, 14 September 2011 (UTC)


 * http://calendarhome.com is based on Wikipedia so the argument is circular.  I fed in October 1582 (which had 21 days) and it told me it had 31.   As for Excel, I entered DATE(1900,4,15) [which was Easter Sunday] into cell A1 and asked it to give me the date of Ash Wednesday (46 days earlier) by typing  A1-46 in cell B1.   The date that came up in cell B1 was 2/29/1900.


 * These date programmes are only as good as the programmers who feed in the information in the first place - they cannot be used as reliable sources.  I've lost count of the times I've fed in a date in one calendar to get its equivalent in another and completely the wrong answer comes out.


 * I didn't say 6 June 6666 would be a Tuesday - I said it was a Tuesday according to the most accurate leap year scheme currently devised.  You, on the other hand, say that it will be a Wednesday with no qualification whatsoever, so that instead of speaking as a mathematician you are now speaking as a fortune teller.


 * There is a growing disparity between solar time (which we use) and atomic time (which scientists use).  They are considering a plan to even things out by dropping the leap year in 5200.   So whichever way you cut it, 6 June 6666 is not going to be a Wednesday.


 * Wikipedia caters for a worldwide audience.  The only country which has adopted the medieval leap year rule is Great Britain.   One of the first things which the newly independent United States did was to repeal this particular piece of legislation in its entirety.   Some countries have gone a stage further and, following advice from their own astronomers, adopted a rule which is completely different. 92.234.23.201 (talk) 18:06, 14 September 2011 (UTC)

(Outdenting) You said 6/6/6666 (Gregorian) is a Tuesday. It is not. This section is about a perpetual Julian and Gregorian Calendar Table, not a table for some unspecified rule that has not been adopted by any standards body, civil, ecclesiastical, or scientific. According to the Gregorian calendar, 6/6/6666 is a Wednesday, not a Tuesday. "They are considering a plan" has no place in an article about what the Gregorian calendar IS. If a Modified Gregorian reckoning is adopted by the appropriate standards body, we should add it to Julian and Gregorian to make a third calendar supported by the table. Even if we were to omit the existing Gregorian rules in favor of the new rules, we'd still have to have something in the table explaining how the new rule operates. Since no such rule exists, we cannot document it. No such reckoning has been enacted by any governing body at all. Your inclusion of an example based on "considering" constitutes Original Research and speculation. The Monster (talk) 18:36, 14 September 2011 (UTC)


 * This issue has already been discussed.  See Talk:Gregorian calendar.   No standards body has charge of the calendar - they can make recommendations but they can't tell countries what to do.   Wikipedia frequently reports proposals and there is no bar on it so doing.   A report of a proposal made by an international organisation, provided it comes from a reliable source, is perfectly admissible.   It is not original research.   However, to meet your objection I have modified the section heading slightly. 92.234.23.201 (talk) 19:54, 14 September 2011 (UTC)


 * Cite ANY country that has adopted a calendar rule by which Gregorian 6/6/6666 is a Tuesday. I can't see any meaningful modification. You still present an example that does not correctly calculate the day of the week under the Gregorian calendar, nor does it cite any government, religious, scientific, or commercial body that has adopted the proposed algorithm as a standard.  If ANYONE has adopted the rule that makes 6/6/6666 a Tuesday, CITE IT.  It is a Wednesday because the rule established in Gregorian calendar makes it a Wednesday.  And if anyone ever does adopt such a rule, it won't be Gregorian anymore; it'll be 201ian.  It'd ALMOST be the Revised Julian Calendar, but it isn't that, either, as the formulae deviate by a day for 100 years out of every 900.
 * Renaming the section "New Style" while retaining references to Gregorian dates in the body is pathetic. You've abandoned any pretense of the table representing a perpetual Gregorian calendar, and instead presented your pet reform proposal as if it were a fait accompli.  This is not appropriate for an encyclopedia.  Commingling this new 2&7/9 algorithm with the existing Gregorian formula, without making absolutely clear what aspects deal with one v. the other, is incredibly confusing. The Monster (talk) 21:03, 14 September 2011 (UTC)
 * Well, that's the point of peer review.  Nobody can get it right first time.   Obviously 6 June 6666 is not a Tuesday in the Gregorian calendar, so I've changed the text in line with your recommendations.   As to whether the modification is meaningful, have you calculated the instant of the vernal equinox in that year?   Since you mention the Revised Julian calendar, yes 6 June 6666 is Tuesday in that as well, and furthermore according to Julian calendar (note 1) it is already slated as a Tuesday in Greece and a number of other countries besides.   To forestall further objection, Wikipedia gives extensive coverage to the proposal to abolish leap seconds, although that has yet to be approved by any of the scientific regulatory bodies. 92.234.23.201 (talk) 17:03, 15 September 2011 (UTC)

(Outdenting again) Whether 6/6/6666 is a Tuesday in the RJC or any other calendar not named "Gregorian" is moot. I see you've thrown the word "Exigian" into the mix, and done a better job of explaining what it is, and how it varies from Gregorian. What countries, religious, scientific, commercial or other standards bodies have adopted this "Exigian" calendar? Giving coverage to a proposal is one thing, but doing it at the expense of covering the existing facts is unacceptable. It is as if you've foregone coverage of the actual winner of last year's Super Bowl to cover the team you think will win the next.

To include this proposed-but-not-yet-adopted Exegian reckoning and exclude the Gregorian system, which is the official calendar of nearly the entire world, (even more nearly the entire English-speaking world; this is en.wikipedia.org) and is the de facto standard even in jurisdictions where some other calendar is officially sanctioned, is not acceptable.

If there were consensus that we should document a perpetual Exigian calendar we could either create a separate table for it, or incorporate it into the Julian/Gregorian table: Here we're just starting to reveal enough of the Hundreds cycle for this Exegian calendar for a clear pattern to emerge, whereas the Julian and Gregorian patterns are far simpler. This is where the short abbreviations you dislike, for month and day of the week, are particularly helpful. If we're going to include Exegian in this article, we ought to see if there's a better way to present it. The complicated system for calculating which '00 years are leap years seems to preclude any kind of compact table presentation.The Monster (talk) 21:17, 15 September 2011 (UTC)

Per the Wikipedia Verifiability policy any mention of "Exigian" should be accompanied by a citation to a reliable source. In the absence of such reliable source(s) the material may be removed by any editor.

In addition, the What Wikipedia is not policy specifies that Wikipedia is not a publisher of reliable original thought, so if 92.234.23.201 made this up, it should be removed. Further, Wikipedia is not a crystal ball, so proposals should not be mentioned unless reliable sources have indicated there is a reasonable possibility of adoption. Jc3s5h (talk) 15:09, 16 September 2011 (UTC)

I noticed that similar material was introduced around a year ago into Hebrew calendar; I have removed it. Jc3s5h (talk) 15:39, 16 September 2011 (UTC)


 * Indeed it does help. Thus far, I've been working mostly to make the article clearer and more accurate.  Now I'm working on changing the tone of the article from "how-to" to something more encylopedic.  There's a certain amount of inherent "how-to-ness" about any article that discusses an algorithm, but I suspect that rewording the article can do a lot to address that issue.
 * I'll see if the Easter calculation can be profitably fit into this article, or whether some other article on the formulae for calculating Easter sufficiently covers the subject that it would be overlap.
 * The principal value I see in treating Julian and Gregorian calendars together is that they can be considered to be species of the same genus: the months of the two calendars have the same names and lengths, and come in the same order. One cannot look at any of the 14 individual 12-month calendars to which this article or Dominical letter refer, and state with certainty "This is a Julian calendar" or "That is a Gregorian calendar".   Three of the four components of the day-of-week calculation are identical for the two calendars, so if there were to be two separate tables, one would be largely redundant.
 * On further reflection, I don't think I'm looking for "printabilty" per se, but concision, of which "printability" is but one aspect. Another is that a person reading the page in a browser should not have to do horizontal or vertical scrolling when viewing a table at a reasonable resolution, unless the information simply cannot be fit into such a form factor.   Making a table larger than it needs to be detracts from clarity if only by making it difficult for someone to see the enough of it at once to get any information from it.
 * Thanks a lot for the opinion. I think it will help make this a much better article.The Monster (talk) 23:52, 17 September 2011 (UTC)


 * Computing the date of Easter is covered in Computus. Jc3s5h (talk) 00:49, 18 September 2011 (UTC)


 * Note: The IP 92. / 84. / 86. is community banned editor -- User:Vote (X) for Change. &mdash; Spaceman  Spiff  18:56, 17 September 2011 (UTC)

"Mental calculation" section
I’ve added the section “Mental calculation” to show the practical method useful to exploit the preceding sections while performing mental calculation. The method, being optimized exactly for this aim, coincides with the preceding sections only at the level of formulas, not at the operative level: therefore it’s needed to explain its operative details also with some examples (the preceding sections can be considered exploitable at the best by computer implementations, surely not by human calculation). The location of the section appears correct since it simply clarifies how to use the preceding formulas with no available calculator (and perhaps spending less time than using a calculator). The page “Determination of the day of the week” is not suitable for locating the method explanation since it describes a wide variety of formulas and methods without concerning mental calculation, while this page “Perpetual calendar” introduces the same tables used by the method (though not optimized for human calculation). Moreover, the section shows the method for both ways a person can “imagine” a week, that is starting with Sunday (like in USA and other nations) or with Monday (about twice the nations with respect to Sunday); the apparent duplication of some parts is due to show the method without elements which can interfere with memorization of the method itself. But after some weeks I found the whole section deleted by (anonymous) 92.233.138.249 with the following explanation: "This is essentially a repetition of the "Perpetual Julian and Gregorian calendar table. Using essentially the same system but starting the week on Monday creates confusion" . These words indicate that he/she was completely missing the aim of the introduced section, not focusing on its optimization for mental use neither considering that many people use Monday as first day of the week.

For these reasons, I reintroduced the deleted section in the same position. Antonio Musarra (talk) 23:38, 25 October 2018 (UTC)
 * , you might like to read about citing a reliable source. Justlettersandnumbers (talk) 09:46, 26 October 2018 (UTC)

I’ve read the note associated with the Undo operation performed on “Mental calculation” section: thanks for the indication; really, the electronic version of Treccani encyclopedia does not include the table (essentially a look-up table) which I saw in a Treccani volume (analogous table is present in the Enciclopedia Europea, but I linked the Treccani thinking to a more well-known encyclopedia for the knowledge origin). Those look-up tables, like the table in section “Perpetual Julian and Gregorian calendar table” of “Perpetual calendar” wiki item or in the first subsection of “Tabular methods to calculate the day of the week” section of “Determination of the day of the week” wiki item, are a condensation in a single table of the concept tables present in section “Concepts” of “Determination of the day of the week” wiki item, which implement the perpetual calendar algorithm. The “Mental calculation” section I had prepared was simply the implementation useful for memorization and use of those concept tables; no further knowledge is inserted in it, it’s only a form of the concept tables suited for memorization, without having those tables written on a sheet of paper in a pocket. Probably, the only link to be added is the one to that section “Concepts” (I had added a different link to avoid a link to the Wikipedia itself, and because the knowledge was already condensed in the table in preceding section “Perpetual Julian and Gregorian calendar table” of the same item). Like in the case of the cited tables, necessarily followed by an example of use, I had added some examples of use (obviously more than one due to the aim of the section). After these explanations, in lack of other objections I think that the section could be inserted with the modified link as discussed.Antonio Musarra (talk) 18:52, 28 October 2018 (UTC)

After six months without contributions/objections/suggestions, I have reinserted the Mental calculation section with the link to the concept tables as discussed. Antonio Musarra (talk) 10:53, 24 April 2019 (UTC)

Day of the week example for 27 January 8315
This has been changed twice by an anon, and reverted twice by me. I'm explaining here in case that anon might be checking the talk page. I'll create a talk page for him and ask him to look at this in case he checks there.

The two changes made so far by the anon can be seen at and. He contends that Wednesday is correct, though the article says it would be Tuesday. I have reverted these two edits. He cites sources, but those sources are for a Gregorian calendar (see, which is the relavent page for a later edition of one specific source he cites). The example he is changing is, as I read the article,for a Revised Julian calendar. I've edited the article a bit to try to make this clearer. Wtmitchell (talk) (earlier Boracay Bill) 22:45, 10 November 2018 (UTC)
 * Yes, I wonder if the Revised Julian calendar details are all that important in this context. Perhaps this stuff should be shunted off into Revised Julian calendar. Thincat (talk) 23:18, 10 November 2018 (UTC)

Reference to October 1582 - just a note from a historian about anachronisms & calendar absolutes between 1582 & 1752
I'm a historian, and I just needed to note in 92.234.23.201's reference to October 1582, it's not a factual absolute that October 1582 only had 21 days. That idea is an anachronism, the irony of which, in a discussion about days and time, boggles my mind.

ONLY if you were a European Roman Catholic did October 1582 have 21 days. If you were French, a European Protestant, or a non-European, October 1582 had 31 days.

This was not a universal change in its time. Therefore, referring to it as a universal change when discussing the calendar is an anachronism.

92.234.23.201, you noted the change in the name of the calendar from Julian to Gregorian without noting the why of the name change, or from where that name comes, and this is important for accuracy. Julian comes from Julius Caesar, of course, but Gregorian comes from POPE GREGORY XIII, at whose direction the new calendar was developed, after centuries of debate and whining within the Church over the matter of miscalculations caused by the Julian calendar, to finally make Easter 1582 retroactively fall on the date prescribed by the 4th century Council of Nicaea. Easter was being celebrated on the wrong day for centuries, but the Church was reticent to do anything about it. The 1562-3 Council of Trent gave the Church the authority to stop the hand-wringing and do something about it. It took a couple more decades, but finally, Pope Gregory XIII, working with Italian scientist Luigi Lilio and Jesuit mathematician/astronomer Christopher Clavius, fixed the calendar problem or problem calendar. The reason they chose October? Any Catholic can tell you, there are no major Holy Days in late October.

However, this was at a time of great unrest in the Christian world. Luther had just posted his 95 Theses in 1517 (ironically, in October); only 2 years after that, you have the rise of Calvinism, then the teachings of Zwingli that lead to Presbyterianism; by 1525, you have the beginnings of the Anabaptists, the Mennonites, etc., etc. Do you think for a moment that they are going to change their calendars just because the POPE says so? Even within the Roman Catholic world, a change that huge wasn't implemented at the same time that the papal bull recommended; France, for instance, waited until the end of the year to make the change.

That's why I'm saying, glossing over the calendar's name change leads to this inaccurate assertion that WORLDWIDE, October 1582 had 21 days. THAT IS JUST NOT ACCURATE.

The changes to the calendar were adopted at different times in different places. This means you CAN'T make blanket statements about days and dates for the past unless you know the geolocation of the matter on which you are speaking. From October 1582 until 1752, you can't generalize about days and dates; 1752 is the latest date I know of that the Gregorian calendar was adopted on the globe, which was by the British Empire.

If you all want to continue to argue about what date June 6, 6666, will be, have at it. That date will mark 4700 years since my Uncle Ronnie's death, by the way, so please remember him on that day, whatever day it is.

But when you speak of the past, between October 1582 and 1752, you are treading on quicksand if you make generalizations. Just look within Wikipedia itself - many famous figures in European history have 2 birthdates in that time period: their Julian birthdate (often called "old style"), and their Gregorian birthdate. Whichever calendar was in use in their geolocation at the time of their birth, that's what day they considered to be their birthdate. It's anachronistic to consider anything else.Kelelain (talk) 14:13, 29 September 2023 (UTC)