Blancpain’s new perpetual calendar timepiece is, perhaps, the perfect microcosm of these efforts. If you happen to own a perpetual calendar, you just had the rare pleasure of watching the date switch from February 29th to March 1st because this year just so happens to be a leap year. In the digital age, such timekeeping idiosyncrasies are trivial but it took some effort to get here. By some, of course we mean a whole lot! Thus, although this story celebrates the new Blancpain Villeret Quantième Perpétuel (which is simply an archaic French term for perpetual calendar), we must set the stage properly for its grand entrance. The mechanical perpetual calendar is, after all, the very summit of what watchmakers have achieved over the course of millennia. Actually, given that digital timekeeping and even the atomic clock are merely the latest and most accurate technical measurements of time that humanity can manage, we posit here that any future measurement technique should be considered a descendant of the humble sundial.

Following on from this, we can say that horology’s key pursuit is timekeeping – to accurately measure and display the time. You may be surprised to hear that even the top executives at watch brands, including Marc A. Hayek over at Blancpain, always tell us that they are in the business of pursuing excellence in chronometry. While this seems straightforward, it is anything but. Instead, timekeeping is perhaps better approached as a multifaceted discipline that requires control over various interrelated factors; chronometry is a big word that encompasses many aspects of watchmaking.

A key challenge lies in the wildly varying scale of things. At one end, time is measured in the fractions of a second, as the balance wheel’s oscillations metre out the watchmaker’s desired interval with its tick-tock rhythm. This precisely regulated subdivision accumulates to count the passing seconds and, in turn, the minutes and hours. The name of the game here is regularity. It informs every aspect of timekeeping at this scale, such as the balance wheel and hairspring’s isochronism, which counteracts the unwinding mainspring’s decreasing torque, as well as the devices’ resistance to temperature and positional changes for improved precision.

In contrast, timekeeping at the largest scales – at least within the context of horology – involves patterns and events spanning months, years, and even centuries, most of them astronomical in nature. Predictable regularity falls away here as bewildering complexity takes its place, held together by myriad rules and exceptions.

Before we hurtle forward and dive deep, it should be noted that this is the second issue in a row that we are looking at calendar mechanisms. Regular readers should therefore expect a bit of a rethread here of the nuts and bolts of the calendar. In other words, here comes another lesson in science and history. As always with our cover stories, if you want to discover the particularities of the Blancpain Villeret Quantième Perpétuel, that bit is actually reserved for the Cover Watch section in the front of the book. That, for example, is where the specifications are. And now, with housekeeping matters and rules of engagement cleared up, on with the show!

Balance and Compromise

Here is the crux of the issue: horology at larger time scales is not just about marking the passage of time. Rather, it must balance society’s need for consistency and convenience with natural phenomena that are rarely so, if ever. Throw historical and cultural influences into the mix, and the watchmaker’s task to bridge these differences becomes clear.

Nowhere is this more apparent than in the perpetual calendar. Before diving into the complexity (and limitations) of this high complication, however, it is necessary to first understand the modern Gregorian calendar that it tracks, as well as the Julian calendar it was based on.

Proposed by Julius Caesar in 46 BCE, the Julian calendar was adopted by the Roman Empire on 1 January 45 BCE, and remained the de facto calendar in the western world for the next 16 centuries. Unlike the lunisolar Roman calendar it replaced, which incorporated both the solar and lunar cycles, the Julian calendar was a solar calendar that was solely based on the earth’s revolution around the sun. Well, it was a geocentric world at that time but you get the idea.

The Julian calendar introduced two crucial changes that remain in place today. The first is the number of days in each month – a curious sequence that sees the consecutive months of July and August having 31 days each, while leaving February with just 28. The reasons for this were complex, and boiled down to a mixture of historical, political, and religious considerations.

Related to the above is the second change: the practice of adding an extra day – the leap day – to February on every leap year. By the advent of the Julian calendar, astronomers had already known for around a century that the solar year was just under 365.25 days. A regular year of 365 days was thus some six hours “short”, which meant that the calendar would accumulate this error and deviate by around a day every four years. The Julian calendar accounted for the shortfall by designating a leap year every four years, when a day was added in February to help the system “catch up”. This mechanism removed the need for manual corrections, which also helped prevent abuse by pontifices who could, under the Roman calendar, lengthen a year to benefit themselves or their allies.

For all intents and purposes, the Julian calendar was accurate enough, hence its continual use for more than 1,600 years. Still, its definition of 365.25 days for a year was an approximation that was not quite right. As it turned out, the solar year’s actual length is 365.2422 days – neither elegant nor convenient, but still reality nonetheless. Consequently, the Julian calendar’s solar year was a tad too long, and the error was accumulating over time. In particular, this affected the observation of Easter; the religious festival’s date was based in part on the March equinox, which was gradually drifting from observed reality.

Things finally came to a head in 1582 with the Gregorian reform, which saw Pope Gregory XIII replacing the Julian calendar with the Gregorian calendar – the system we still use today. The single biggest improvement introduced by the Gregorian calendar was its spacing of the leap years. Rather than designating every fourth year as a leap year, a more complex set of rules was implemented to reduce the Julian calendar’s error.

Under the Gregorian calendar, years that are divisible by 4 are designated as leap years unless they are also divisible by 100, in which case they are regular years. The exception to this exception is if a year is also divisible by 400 – if so, then it is a leap year. 1800 and 1900 were thus regular years, while 2000 was a leap year. Looking forward, 2100, 2200, and 2300 are all regular years, and 2400 will be a leap year.

The Gregorian year’s tweaked algorithm offers an upgrade to the Julian calendar by averaging the solar year to 365.2425 days instead, which reduces the error to a nearly imperceptible 26 seconds a year. For civil use, it is essentially perfect.

Counting The Days

Where does this lengthy preamble leave us? Hopefully, with a better appreciation of how the modern calendar and its quirks came to be, as well as a glimpse at the challenges of engineering a device that can keep track of these peculiarities. But let us not get ahead of ourselves, and build our perpetual calendar up from the basics.

From a reductionist perspective, a calendar complication is simply a set of wheels and levers that advance its display(s) once a day at midnight to show the new date and, occasionally, other information such as the day of the week. Indeed, the simple calendar does exactly this with a 31-day date wheel. As its name suggests, however, the complication is fairly simple, and does not account for the differing lengths of the months. So, it requires a manual correction at the end of every February, April, June, September, and October, in order to advance the date from the 30th to the 1st of the following month.

The upgrade to this is the annual calendar, a complication that is so named because it only requires a correction once a year, at the end of every February. The annual calendar is built in different ways by different manufactures. The underlying principle is the same though: by adding a series of components, including a wheel with five longer teeth or a disk with five deeper notches, a mechanical computer that more closely models the same five months is created. The computer’s “input” here varies according to the length of the teeth or the depth of the notches, which engage differently with the fingers and gears they are connected with. As for the “output”? It is the crucial difference between advancing the date wheel by a single day, such as on the end of 31st August, versus a double jump that goes from the 30th in a “short” month to the 1st of the next.

Alas, February’s varying length is beyond the capabilities of the annual calendar’s mechanical computer. The next step up is the perpetual calendar, which goes further by accounting for February’s uneven number of days. Unsurprising, its complexity qualifies it as a high complication and a hallmark of haute horlogerie.

Like the annual calendar, the perpetual calendar functions like a mechanical computer, and can be realised in different ways. The very first one is attributed to English watchmaker Thomas Mudge, whose 1762 pocket watch is the first known example of this complication in any kind of timepiece. You can see it for yourself at the famed British Museum in London, as the editor has. The basic design of the perpetual calendar is evident in this very watch, which can be neatly summarised for most contemporary watches that follow the most traditional approach. Perpetual calendar mechanisms are built around the grand lever, which is an outsized, multi-pronged lever that “reads” the programmed “inputs” and translates them to “outputs” by advancing the date wheel.

There are variations on this theme, of course. The month wheel may have 12 notches, for instance, and rely on a separate wheel – or Maltese Cross-shaped component – to track the leap year. Alternatively, it may just have 48 notches instead, each corresponding to a month in the same 4-year cycle. This, as noted above, covers just the classic iterations of the complication; other mechanical designs for the perpetual calendar exist and we may come back to this complication in a more in-depth style later this year.

Whatever its design, the perpetual calendar represents a significantly bigger jump in technical complexity compared with the full calendar and even the annual calendar (although that complication as much newer but we digress). As you may recall, the Gregorian calendar excludes three leap years in every 400-year cycle, with the next ones being 2100, 2200, and 2300. Assuming that a perpetual calendar timepiece is kept running and requires no maintenance – one can dream – it will only need three adjustments every 400 years.

Mechanical considerations aside, how the various pieces of information are displayed on the dial is another challenge. Legibility and aesthetics are, after all, determined by the arrangement of components and displays, which is influenced to some extent by movement architecture, but also by design choices. The last major piece of the puzzle concerns wearability. Since the typical perpetual calendar is built as a module that is then stacked atop a base movement (the module is literally mounted dial-side, just as all conventional calendar indications are), finesse is necessary, lest an overly thick movement is created to yield a timepiece that is unwieldy on the wrist.

A Verdant Touch

Long renowned for its calendar watches, Blancpain has developed a deep expertise in this segment that extends to even the esoteric Chinese calendar. Perpetual calendars, in particular, are well-loved staples within the brand’s line-up. Among them, the Villeret Quantième Perpétuel stands out and has existed in its current form since 2018, although the perpetual calendar has been making the rounds for the brand for years before that. Elegant, functional, and perfectly proportioned, the Villeret Quantième Perpétuel offers a masterclass in the execution of the high complication, from technical elements to design considerations and more.

This year, the Villeret model (no other Blancpain collection features a perpetual calendar) welcomes a new reference in red gold and, for the first time, a green dial. Inspired by the fir trees lining Blancpain’s native village of Villeret <there is an entire story about Villeret and La Brassus that we do not have the time to get into here but you can get a sense of this history – and the brand’s fascinating story – in our Spring cover story last on the Fifty Fathoms – Ed>, the new colourway does not just freshen things up by offering an alternative to the current references with white or blue dials. Instead, it also proposes a more contemporary style of refinement that connoisseurs will surely appreciate.

At first glance, what is immediately striking is the dial’s symmetric layout. Here, the various counters are spaced comfortably across the dial, with the respective displays presenting information according to their relative importance. To that end, the display of time is reserved for the three feuille hands sweeping across the dial. Meanwhile, the current day and date are each tracked on corresponding sub-dials – at nine and three o’clock. As for the less frequently used month and leap year indicators? These displays have been relegated to 12 o’clock, where they share a single counter that, nonetheless, offers at-a-glance legibility.

Familiar Phases

If the perpetual calendar tracks the date of the Gregorian calendar based on the earth’s orbit around the sun, then surely its counterpart – the moon, our closest celestial companion – deserves a place on the watch dial as well. Indeed, the moon phase display is an oft-included complication on timepieces with perpetual calendars, and it sits here at six o’clock.

A discussion of the lunar cycle is well beyond the scope of this story. Suffice it to say, however, that like Earth’s orbit around the sun, it is an unruly phenomenon that defies simple calculations, as the synodic lunar month is 29.530588 mean solar days long. So, the same game of approximation is played here: to display the phases of the moon on a watch, the lunar month is typically coded mechanically using a 59-tooth wheel to represent two lunar cycles. Advancing the wheel by one tooth daily creates a lunar month that is 29.5-days long, which is just 44 minutes and 2.9 seconds short of the actual lunar cycle. This deviation accumulates to an error of one day every 2.5 years and, by extension, a correction in just as long.

For Blancpain, this complication is especially dear. The reasons are historical: when modern Blancpain reemerged in the early 1980s, towards the end of the Quartz Crisis, the moon phase display was arguably its anchoring complication. Swiss brands had, until then, largely attempted to compete with quartz movements on price, by stripping away complications and simplifying their mechanical calibres. This strategy was, in hindsight, largely ineffectual.

Blancpain, on the other hand, took a contrarian approach by leaning into the complexities of mechanical watchmaking, and released its first watch with a moon phase display in 1983. The timepiece’s debut was a watershed moment; the complication harked back to the rich legacy of mechanical timekeeping, and showcased a romantic side of traditional watchmaking absent in quartz timepieces. This particular watch did more than just galvanise the wider Swiss watch industry. Rather, it also established the complete calendar (i.e. a simple calendar that shows the day, date, and month) with moon phase as a Blancpain signature, and introduced the manufacturer’s “man in the moon” design that remains in use today.

Aesthetic Appeal

Despite needing to display multiple pieces of information from the perpetual calendar and moon phase, the Villeret Quantième Perpétuel is still eminently legible. Part of the credit should go to the movement designers, of course. Readability is also subtly enhanced with contrasting textures on the dial, which creates varied surfaces that light plays across differently. Note, for instance, how the main dial’s sunray finish serves as a background against which the snailed sub-dials sit – with the latter rendered in two layers, no less.

Other details abound if one knows where to look. Consider the design of the three central hands and how they are mounted to the cannon pinion. Eagle-eyed observers will note how they form a stepped pattern of concentric circles right at the centre of the dial – an attractive yet subtle touch that mirrors and complements the stepped bezel emerging from the case. In much the same way, the hands and appliqué indices have all been rendered in polished red gold to speak a uniform visual language.

High Calibre

The heart of every watch is its movement, and the one powering the Villeret Quantième Perpétuel is Blancpain’s self-winding Calibre 5954. Some of its technical features have already been discussed above, from its organisation of information on the dial to its inclusion of the moon phase display.

What is also important are the movement’s dimensions. At just 4.97mm high, Calibre 5954 can be considered an ultra-thin perpetual calendar movement. This feature translates to an equally svelte case, which enables the Villeret Quantième Perpétuel to clock in at just 10.80mm high – slim enough to slip under a shirt cuff effortlessly. Despite its diminutive dimensions, Calibre 5954 still manages to have a full-size rotor for greater efficiency when winding its barrel and has a longish 72-hour power reserve. A temperature- and shock-resistant silicon hairspring is par for the course here, naturally.

What is also of note here is how the watch’s indicators are adjusted. The usual implementation involves positioning recessed pushers around the case – to adjust a particular display, one simply uses a stylus or any similar tool to actuate its corresponding quick-set pusher. This presents two problems though. For one, making corrections is inconvenient as a tool must be on hand. The second issue concerns aesthetics: the pushers on the case interrupt its visual continuity.

Blancpain overcame this issue with an ingenious solution – under-lug correctors that can simply be actuated using one’s fingers, not unlike a chronograph pusher. These correctors are invisible when the watch is worn, which also creates a more harmonious case. Convenience and design aside, it is also worth noting that the correctors are blocked when the indicators are changing, which prevents the wearer from accidentally damaging the movement. Fans of the Blancpain system will recall it has been in action for almost 20 years now.

The overall result here is a timepiece that is complex under the dial, but easy to read and operate. Perhaps what makes things even more poetic is the fact that 2024, its year of release, is a leap year. What better way is there to mark the occasion, than with a new perpetual calendar?

This article first appeared on WOW’s Spring 2024 issue.

For more on the latest in watch reads, click here.