written by:
Ornatus Mundi
published:
2024-03-01
categories:
Bulgari, Franck Muller, IWC Schaffhausen, Jaeger-LeCoultre, Kurt Klaus, Ludwig Oechslin, MIH Watch, Miki Eleta, snapshot, Stephen McDonnell, Svend Andersen, watches, watchmakers, Zenith
Snapshot(s): The Battle of Calendars – Leap Year Challenge
Let’s watch how a simple (Bvlgari), a complete (vintage JLC), an annual (MIH Watch), and a perpetual calendar (IWC Da Vinci) make it through ‘The Day’ of a leap year!
2024 is once more a leap year with its 29th of February, and for us collectors this means worship time involving a night spent awake watching our perpetual calendars doing their mechanical magic. Pure nerd stuff (since we all know what’s happening anyway), but this is essentially aficionados doing aficionado things.
For those of you who didn’t have the time or opportunity to do so – here’s our special service for you – we followed the main types of calendars through over 48h of the leap year transition. But first, let’s go back and tackle the theory behind!
Background: Lunar and Solar Cycles:
When humankind tries to make sense of the universe and translate those of its peculiarities that affect the organisation of daily life into practically manageable (and religiously acceptable… but let’s leave that for the moment…) rules. Often enough those are approximations, and by their very nature approximations come with a certain degree of imprecision. Over time, such imprecisions yield unacceptable deviations from observable reality, and need be corrected.
This brings us to one of the most fascinating correction concepts that has been developed over time, the calendar. Why is that so?
Sidenote: The challenge lies in the fact that the two main celestial objects important to mankind have quite different cycles: the moon which orbits earth with a cycle of 27.322 days, while the earth itself orbits the sun during exactly 365.2422 days (during which it rotates on its own axis by 360° each 24h), which is known as the Solar Year. As the former cycle (roughly) determines months and the latter the year, the quest for astronomers was always to reconcile the two cycles in practicable ways.
(Sideral and solar years. Image © study.com)
Early (lunisolar) calendars were often based on the lunar cycle and worked with a thirteenth, called intercalary or leap month to restore alignment with seasons and thus the solar cycle. Intercalary months followed complex calculations and came with a certain flexibility in terms of their occurrence and length. Such lunisolar calendar was also used in the Roman Empire, where the terms of office for members of the magistrate were based on the calendar. Since the occurrence of intercalary months was complicated and frequently required a deliberate decision, it was a means of exercising power as well – it could shorten or lengthen the magistrates’ terms. The Julian Calendar instituted in the year 46 BC by Roman emperor Julius Caesar brought a first workable approximation devoid of any human manipulation by having three normal years of 365 days followed by a leap year of 366 days (its additional leap day was called bissextus), such that on average a year has 365.25 days.
However, if one compares the average year’s lengths between the Julian Calendar and the Solar Year one realises that over centuries the former would be off by about 3 days every 400 years. This is slow enough not to bother in day-to-day life, unless… religious considerations come into play: for the Catholic Church, the date of Easter, a movable feast, is celebrated on the first Sunday after the Paschal full moon, which is the first full moon on or after 21 March of each year, the nominal date of the vernal (or spring) equinox. Thus, from a Catholic point of view it was desirable to have that date drift as little as possible from the solar equinox. The reform to the calendar was set in motion through the authorisation of Pope Paul III by the Council of Trent in 1545 and caused a nearly 30-year period of fascinating astronomical and mathematical debate amongst the most prominent scientists of the time, including Tycho Brahe (known for his impressively accurate astronomical observations and constructor of the first observatory in Christianity), Aloysius Lilius, Italian astronomer and physician who drafted the final proposal of the new calendar, and finally Christopher Clavius, a Jesuit German mathematician who as member of the Vatican commission first accepted Lilius’ proposed calendar. The new calendar was based on the Julian Calendar and provided for the following modifications in respect to leap years:
“Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 are not leap years, but the year 2000 is.”
(Source: United States Naval Observatory)
This shortened a calendar year by 0.0075 days, effectively reducing the gain to just 0.1 day over 400 years. Essentially, the calendar repeats completely every 400 years, during which 303 years are regular ones of 365 days and 97 are leap years of 366 days. Still not perfect, but only one day in 3322 years off.
(The first authorised print of the Gregorian Calendar by Vincenzo Accolti in 1582; image © Wikipedia)
The new calendar was instituted in 1582 by Pope Gregory XIII through the Papal Bull ‘Inter Gravissimas’, and implicitly this meant also the ultimate acceptance of the heliocentric system by the Catholic church. The calendar was later named after the pope as Gregorian Calendar. Even though the Papal Bull had legal effect only in Catholic countries, with protestant ones initially rejecting it, today it is the most widely followed calendar with only 5 countries (Afghanistan, Iran, Saudi Arabia, Ethiopia, and Nepal) not having adopted it (yet).
Fast forward to today, the 29th of February 2024 – which according to above rules is a leap year having a leap day. For horological connoisseurs this is one of the high times in collecting and appreciating, as this is the day when we live to appreciate the mechanical mastery of one complication that above mentioned (mechanical) approximations or universal characteristics to manageable mechanisms: the perpetual calendar.
(Perpetual calendar mechanism from IWC; image © IWC)
Such a calendar mechanism accounts for the different lengths of the months throughout a year, that is for the 28-, 30- and 31-day long months as well as, every 4th year, for the 29th day of February. It is based on but does not fully comply to the Gregorian calendar in as much as it does not account for the leap year exception in those years fully divisible by 100 but not by 400 (e.g., last time the year 1900), meaning that a manual intervention is necessary next time in the year 2100. It is such not completely ‘perpetual’ (only Svend Andersen’s “Perpetual Secular” as well as the super-complicated Franck Muller Aeternitas Mega come to mind).
(Franck Muller’s impressive Aeternitas Mega features a truly perpetual calendar which that can correctly display leap years on 4 years, no leap years on 100 years, leap years on 400 years)
Most perpetual calendar mechanisms use a 31-days-month as base and switch dates further on shorter months. The only perpetual calendar we know of to use a 28-days-month as base is the MB&F Legacy Machine Perpetual, developed by independent watchmaker Stephen McDonnell.
Simpler calendar mechanism include the annual calendar, which accounts for long (31 days) and shorter (30 days) months, but not for February in any form (this means it needs to be manually set once/year), complete calendars which show month and weekday in addition to date, but always go a full 31-day cycle for the latter (requiring correction every 2nd month), and common date-only mechanisms to which the last characteristic for complete calendars also applies.
The Contestants:
Before going on to the actual competition, let me present our contestants in a few words:
Simple Date: Bvlgari Diagono Scuba SD38S
On paper, this looks like a mundane watch, but with some watchmaking interest: a 38mm stainless steel diver’s version of the Diagono line of watches, presented in 1994, water resistant to 200m, equipped with a COSC-certified ETA 2892A automatic movement. The case is a fantastic example of superb Italian functional design, in fact I called it a ‘Masterpiece of (Italian) Brutalism’. For more, see here.
Complete Calendar: Jaeger-LeCoultre Triple Calendar Ref. 2721*
This watch is a fairly new addition to the stable. It is already 80 years old, but its design with the lovely, soldered teardrop lugs hasn’t aged a day, so it seems. A 36mm fine example of timeless classicism from JLC (‘the watchmakers’ watchmaker’), driven by the Cal. 464/A which shows a central date as well as month and weekday in a harmonious arrangement with a small second at 6 o’clock. The archetypical movement is used as base for the corresponding Vacheron Constantin calendar watches as well.
Annual Calendar: The MIH Watch
The first watch that was clearly based on Ludwig Oechslin’s ‘simplification as complication’ approach was realised by a ‘dream team’ consisting further of Paul Gerber, Christian Gafner and Beat Weinmann. It paved the way for a different appreciation to watchmaking, putting the intellectual effort of making things as simple as possible to the fore. The annual calendar mechanism used only 9 moving parts (only gears and wheels) and is fully operated by the crown. For more, see here.
Perpetual calendar: IWC Da Vinci Tourbillon**
Mechanically, the watch is defined by a perpetual calendar developed by IWC’s famous master watchmaker Kurt Klaus already in 1985. It was revolutionary in the sense that it could be fully set by the crown. In consequence, this also meant that all calendar indications were mechanically synchronised – making setting even easier and obliterating the need for a leap year indication. Further delights are the true ‘full calendar’ mechanism which shows the complete year as well, and – in this specific model – a flying tourbillon developed by Richard Habring.
What this also means is that nothing spoils the case sides with holes for corrective pushers. Hanno Burtscher came up with a congenial case design which highlights this perfectly.
The Battle:
That theoretical and technical background aside, let’s have some fun and compare how the different types of calendars behave on ‘The Day’ in a leap year. In the following, I am posting images showing the various calendars’ advancements over a 48h period starting with 28th of February and note their respective advancements and the correctness of the indications.
28th of February – 08:20:
Here the initial situation – the watches are set to the same time and correctly to (all of) their respective date indications for today in the year 2024:
- Simple Date: date correct
- Complete Calendar: date, weekday, month correct
- Annual Calendar: date, month correct
- Perpetual calendar: date, weekday, month, year indication correct
29th of February – 08:20:
All watches show the correct date, weekday and month. No surprise for either the simple date, complete or annual calendars, but for the perpetual this shows it was correctly set to indicate a leap year:
- Simple Date: date correct
- Complete Calendar: date, weekday, month correct
- Annual Calendar: date, month correct
- Perpetual calendar: date, weekday, month, year indication correct
29th of February – 21:30 – 23:40:
We start to see the first difference between the calendars: the IWC starts to advance the date by two days to account for the shorter February. This additional switching is completed by 23:40, and the watch now shows 31st February 2024. Also, the MIH Watch starts moving the date at 23:00, but this is a normal date move, and it stops at 30th February. The JLC now begins to advance the weekday:
- Simple Date: date correct
- Complete Calendar: date, weekday, month correct
- Annual Calendar: date correct, month wrong
- Perpetual calendar: date wrong, weekday, month, year indication correct
29th of February – 23:59:
Just a minute before March begins, we’re now witnessing the final (and totally normal) switch of the calendars of all calendars which is completed just seconds before midnight, with the exception of the MIH watch which, due to using only gears, takes 10min more. As expected, at the end only the perpetual calendar correctly transitioned to 1st March 2024. All other watches show a non-existing 30th of February.
- Simple Date: date wrong
- Complete Calendar: date wrong, weekday correct, month wrong
- Annual Calendar: date wrong, month wrong
- Perpetual calendar: date, weekday, month, year indication correct
Just for the fun of it, we manually advance the MIH watch which in contrast to the IWC corrects for shorter months after the normal date change, and this happens between 01:20 and 02:00 in the night:
1st of March – 08:20:
I also manually set the simple and the complete date watches (for the latter this means just a few ticks with a toothpick on actuators in the case side), and all watches again are set and ready for the next 8 weeks, at least…
Observing the transition
Overall: it was fascinating to compare the different calendar concepts. Although the article is called ‘battle’, this is not about singling out a ‘winner’ – that one was clear from the outset. But knowing a bit about the different constructions and the challenges the watchmakers faced, it was a great experience which one gets to fully enjoy only every 4th year! Just one fascinating bit: to account for shorter and longer months, the MIH Watch and the IWC Da Vinci have different approaches: while the former corrects after the normal date change.
The philosophical context of perpetual calendars is fascinating and marks the conclusion of one of the fiercest disputes in recent history: with the Gregorian calendar the heliocentric view on the universe finally and officially prevailed over the geocentric one. To commemorate this, I’d like to show a clock made by horological philosopher, Miki Eleta: The ‘Svemir’ (eng.: universe) combines both heliocentric and geocentric models into one single mechanism:
The Svemir is centred around the blue earth, with the geocentric indications being the worldtime ring and the ring indicating the path of the sun around the earth, while diagonally above the heliocentric system is placed, with its own sun and six planets (Mercury, Venus, Earth, Mars, Jupiter and Saturn). A central clockwork drives all those indications!
With that, all that remains now is the look forward four years to the next leap day to come!
Ornatus Mundi
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*) I know: this watch deserves (and will get!) a separate article soon
**) dito…