Days of the Year

An in-depth look At the one horo­log­i­cAl com­pli­cA­tion we use the most And its ex­tended fAm­ily

DA MAN - Caliber - - MECHANISM -

Among the many me­chan­i­cal com­pli­ca­tions in a watch, the most com­mon and use­ful one—and per­haps also the most un­der­ap­pre­ci­ated va­ri­ety—are cal­en­dars. In the realm of fine watch­mak­ing, how­ever, cal­en­dar com­pli­ca­tions en­com­pass much, much more than sim­ple day/date dis­plays. In fact, you’ve likely heard of terms like “per­pet­ual cal­en­dar,” “an­nual cal­en­dars” and so on. So, be­low, we will take you on a brief tour of the com­pli­ca­tion fam­ily bring­ing the days of the year to your wrist.


At the low­est tier of the cal­en­dar com­pli­ca­tion fam­ily we have the sim­ple date win­dow. Fol­low­ing this is the day-date in­di­ca­tor with two aper­tures, one for the name of the day and the date. It should be noted, how­ever, that th­ese ba­sic mech­a­nisms do not take the month into ac­count. In other words, th­ese watches al­ways op­er­ate on a 31-day cy­cle, forc­ing the owner to man­u­ally ad­just the dates at the end of ev­ery 30-day month as well as at the end of Fe­bru­ary.

An­other step up and we have the com­plete cal­en­dar, some­times also called the triple cal­en­dar sim­ply be­cause it in­di­cates three bits of in­for­ma­tion: day, date and month. Still, this cat­e­gory of watches still doesn’t take dif­fer­ing month lengths into ac­count, and man­ual ad­just­ment will be nec­es­sary at the end of cer­tain months.

Of course, slight vari­a­tions of pre­sen­ta­tion based on th­ese ba­sic con­cepts also ex­ist. Some watches, for in­stance, em­pha­size the date dis­play by us­ing large, dou­ble aper­tures with the left win­dow dis­play­ing 0 to 3 and the right 0 to 9. Oth­ers use a small sub-dial to in­di­cate the date of the month or an ex­tra hand that points to dates placed along the out­side pe­riph­ery of the dial. The lat­ter is some­times known as a “Bankers” date dis­play.


From here on, things get much more com­pli­cated, but also much more fas­ci­nat­ing. So, step­ping up from the com­plete cal­en­dar we have the an­nual cal­en­dar. Put sim­ply, an an­nual cal­en­dar “knows” which months end on the 30th and which ones run un­til the 31st. The prob­lem, how­ever, is Fe­bru­ary. You can blame the An­cient Ro­mans for the mess with Fe­bru­ary, but what this means for us to­day is that if you have a watch with an an­nual cal­en­dar com­pli­ca­tion, you still have to man­u­ally ad­just the date dis­play at the end of ev­ery Fe­bru­ary.

For­tu­nately, the next tier of cal­en­dar com­pli­ca­tions knows how to deal with the pesky sec­ond month. We are, of course, talk­ing about per­pet­ual cal­en­dars. Also known as the the per­pet­ual cal­en­dar is ac­tu­ally con­sid­ered grand com­pli­ca­tion due to its sheer com­plex­ity. As the name im­plies, a per­pet­ual cal­en­dar can track the cor­rect date per­pet­u­ally. Well, at least un­til 2100 that is.

Here we come face to face with yet an­other quirk of the Gre­go­rian cal­en­dar— one that is per­haps a bit lesser known. See, we are all fa­mil­iar with leap years, right? Ev­ery four years, we add an ex­tra day to Fe­bru­ary. The thing is, not ev­ery year di­vis­i­ble by four counts as a leap year: If a year is di­vis­i­ble by 100 but by 400, then it’s counted as a nor­mal year. So, 2000 was a leap year, but 2100 won’t be. For this added com­plex­ity, you can thank Pope Gre­gory XIII—although he did so in an at­tempt to fix the mess left by the Ro­mans, so he’s not en­tirely to blame, we guess.

Back to the per­pet­ual cal­en­dar, the ba­sic mech­a­nism of this com­pli­ca­tion has a “me­chan­i­cal mem­ory” of 1,461 days, or four years in­clud­ing one Fe­bru­ary 29th. Left on its own, a per­pet­ual cal­en­dar watch will es­sen­tially show the cor­rect date for the fore­see­able fu­ture. Sure, it will need

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