A simple date display is a pretty handy thing. This Rolex innovation that has been adopted in almost every watch sold, tells us where we are in the month, provided one is conscientious enough to keep it properly set, to account for every month that isn’t 31 days in length. This need to periodically set the date has driven some watch wearers to simply let the date display do whatever it wants, while those with OCD who haven’t been driven nuts are quietly pushing up the demand for watches without a date display.

But why not have it all — a date display that always tells the correct date, minus all the fiddling? Should be worth its weight in gold in the age of Fake News. And that’s exactly what a perpetual calendar does, automatically displaying the correct date on months with 31, 30, 28 days, and it even remembers to add a 29th day in February for leap years, as long as the watch is wound and ticking, in perpetuity… till 2100.

The Fault in Our Stars: The Non-Discrete Universe

If anyone asks, we are using the Gregorian calendar of 1582, itself an improvement of the Julian calendar of 45 BC that was instituted by the very same Julius Caesar who was stabbed by Brutus the following year.

The Gregorian is such a wonderful calendar that we date everything from events to receipts without giving it a second thought. That wasn’t the case before. There was a time in the distant past when the calendar would drift out of sync with the stars so much that knowing the date didn’t mean not being confused about it. Seasons change, and this is the objective reality of 365.24219 days for the average tropical year (the duration of the earth’s orbit around the sun) upon which a calendar has to be anchored so that activities such as agriculture can be ordered accordingly, objectively.

Among his many contributions, Julius Ceasar reformed the calendar
Among his many contributions, Julius Ceasar reformed the calendar

Before Julius Caesar’s calendar reform, the Roman calendar had 355 days. To match what was happening in the skies, an intercalary month of 22 or 23 days would be inserted between February and March (the way we add one day every four years to February), ideally every other year to approximate the actual length of the tropical year. But in reality, the intercalations were added irregularly by discretionary decree, and this caused a lot of confusion. Have the authorities added the intercalary month? Are we still in February? Or is it already March? Are we meeting tomorrow? An error correction of 20-odd days was a sledgehammer answer to something best achieved with a nudge.

Coming to the rescue, the Julian calendar designates the length of the year at 365.25 days, which is much closer to the actual figure, so every year has 365 days on the calendar, and an extra day (instead of a near-month) is added every fourth year to account for the extra 0.25, much like we do today.

The Gregorian calendar introduced by Pope Gregory XIII in 1582 which we use today has the year at 365.2425 days. Going even closer to the actual figure of the tropical year means there is even less deviation over time than the Julian calendar. A year is 365 days on the calendar, and the 0.24 deviation is addressed by adding 1 day to February, every four years. This in itself is an annual over-compensation of 0.01 (we rounded off the 0.24 to 0.25 to add 1 day in four years), which adds up to a full day every 100th year: that is why in 2100, though a leap year, we do not add the extra day.

Pope Gregory XIII introduced the Gregorian calendar in 1582
Pope Gregory XIII introduced the Gregorian calendar in 1582

That is why in 2100, a mechanical perpetual calendar the likes of which we have today, will stumble. It will faithfully show Feb 29 every leap year as prescribed, but shuffling back in 2100 like a cha cha, is extra service without a tip. Nevertheless, we bet watchmakers are working on it, and it doesn’t change our belief that a perpetual calendar is the smartest, most useful complication that should have a place on our wrists.

Buyers Aware: Technical Evolution

The world’s first wristwatch perpetual calendar came about in 1925 when a Patek Philippe movement (serial 97975) for a women’s pendant watch was re-cased for wearing on the wrist. Its four subdials displayed the day, month, moon phase and small seconds, with date pointed along a scale at dial perimeter.

First perpetual calendar wristwatch, 1925
First perpetual calendar wristwatch, 1925

The first ‘true’ wristwatch perpetual calendar, i.e. one with a movement made for the very purpose as opposed to a converted pocket watch movement, is probably the Breguet no. 2516. In white gold tonneau case, it was made in 1929 and sold to Jean Dollfus in 1934 for CHF 11,000, and resurfaced at Christie’s in 2011 where it was auctioned for CHF423,000. No less extraordinary than the 40x bump in price, is the watch’s instantaneous jump capability, where all calendar functions advance in the same instant. It’s a feat not common even among modern-day perpetual calendars.

Breguet no. 2516 (Image © Christie’s)
Breguet no. 2516 (Image © Christie’s)

The first serially produced perpetual calendar would arrive a decade later in 1941, Patek Philippe’s ref. 1526 in 34mm gold case, of which 210 pieces were made over a span of 12 years.

Vintage Patek Ref 1526 (Image © Christie’s)
Vintage Patek Ref 1526 (Image © Christie’s)

Get Synchronized

For a time, perpetual calendars were the preserve of the top watchmaking companies the likes of Patek Philippe, Vacheron Constantin, Audemars Piguet, Jaeger-LeCoultre because they were exceedingly complex and very expensive to produce. They were also pretty fussy to operate: every item of calendar information that a perpetual calendar tracked had to be set by toggling recessed pushers set into the case with the use of a stylus.

That is, until IWC decided it wasn’t having any of this and barged onto the scene with the 1985 Da Vinci (IW3750), the first perpetual calendar with synchronized display, where all information is advanced in synchrony, via just the crown.

IWC Da Vinci (1985)
IWC Da Vinci (1985)

Not only was it far easier to use than earlier non-synchronized perpetual calendars, it also cost less, being designed for serial production from ground up. Another neat feature about the Da Vinci that we’re amazed more brands don’t adopt is the 4-digit year display. Affords a sense of completion, does it not? Read more about the Da Vinci here.

Ulysse Nardin Perpetual Calendar Ludwig (Image © Christie’s)
Ulysse Nardin Perpetual Calendar Ludwig (Image © Christie’s)

Like Moonwalking

Following IWC’s charge, more advancements have followed to populate the field of perpetual calendars with greater diversity. Among these, a significant innovation is Ulysse Nardin’s Perpetual Ludwig. It is named for historian and horologist Dr Ludwig Oechlin whose collaboration with the brand produced other technical icons like the Trilogy of Time series of astronomical complications, and the Freak.

While the Da Vinci scores with the elegant simplicity of controlling all setting from the single crown, the calendar displays cannot be set backwards: if one accidentally sets the date too far ahead, or crossed enough time zones east to west to require a date correction backwards, the only course is to pull the crown (stop the watch) and wait for the day to catch up.

The Perpetual Ludwig’s solution to this problem is an ancient planetary gear system called “epicycloidal gears” which Dr Ludwig discovered while restoring an ancient clock. Instead of relying on conventional springs and levers to drive the calendar indications one-way, the use of gears instead allows the Perpetual Ludwig’s synchronized calendar displays to be set forward or backwards without fuss.

Then there is this mechanical version of the Millennium Bug: there is no February 29 in the year 2100. While every synchronized perpetual calendar will have to be sent back to the factory for adjustment, the Perpetual Ludwig can simply be advanced to March 1 by the wearer, and then the day independently set backwards by one.

Greased Lightning

Nevertheless, there is a chink in the Perpetual Ludwig’s impressive amour, and that is the non-instantaneous date change. At the end of a 30-day month, the date jumps to 31 at 9pm, before jumping to 1 at midnight. On a non-leap year, the date jumps to 29 at 9pm, 30 at 10pm, 31 at 11pm, and finally 1 at midnight. In these two instances the watch is showing the wrong date for three hours as it transits towards the correct date.

This issue is rectified in the H. Moser & Cie. Perpetual 1’s “flash calendar”. The Perpetual 1 is synchronized like the Da Vinci, can be set forward and backwards like the Perpetual Ludwig, and boasts a unique display that is extremely, sublimely succinct. There is no moon phase, neither a day display, just an oversized date window that always shows the correct date, while the 12 hour indexes pull double duty as month markers indicated by a short central hand.

For instant date changes regardless of the number of days in the month, it uses two date rings instead of the usual one, stacked one above the other, arrayed in a relay.

The top ring (nearest to the dial surface) displays 1-15 followed by a window, through which the bottom ring showing 15-31 can be read. In the latter part of the month, the top ring is hence stationary as the bottom ring advances through the dates. At the end of the month, the top ring makes a single jump to the first day of the following month, instead of the several jumps needed if only one date ring were used.

Some Models

Whichever model one chooses on the evolutionary ladder of perpetual calendars, one is assured that one thing unifies them all: unparalleled utility. The perpetual calendar is simply one of the smartest mechanical complications, of unparalleled utility. Below, are some models one should consider when acquiring one.

IWC GST Aquatimer Perpetual Calendar IW3756
The much-loved GST (“gold, steel, titanium”) series of sports watches was produced from 1997 to 2004. Models included chronograph, rattrapante, diver’s watch with water resistance up to 2,000 meters, Automatic Alarm, and the titanium-cased GST Deep One, the world’s first diver’s watch with a mechanical depth gauge. The GST Aquatimer perpetual calendar was produced from 2001-2004, in 44mm steel or titanium case with a variety of dials (silver, white, black, salmon), and also features a chronograph. It is driven by cal. 79261 which consist of the self-winding ETA 7750 chronograph movement with a synchronized perpetual calendar module which debuted in the IWC Da Vinci. Water resistant to 120 meters, with 44 hours of power reserve.

IWC Da Vinci Perpetual Calendar IW3762 
A departure from the round case of the 1984 original, the Da Vinci collection returned in 2007 as a tonneau that traded classical finesse for a massive jolt of alpha-male charisma. Driven by cal. 79261 described above, the perpetual calendar debut that same year as the ‘Edition Kurt Klaus’ in platinum (50 pieces), rose gold (500 pieces) and stainless steel (3,000 pieces). A rose gold version with black dial was launched in 2009 (1,000 pieces) followed by a non-limited version in stainless steel that was produced from 2011-2015. The Da Vinci collection has since returned to the round case as of 2016.

Royal Oak Perpetual Calendar Ref. 26574
No self-respecting rapper seems to be without one; except that it would have to be breaded in diamonds. For the rest of us, the Royal Oak perpetual calendar’s faceted beauty embodies that golden ratio of elegance, sophistication and function. Produced from 2015, this reference features a week counter in addition to the usual calendar displays and a photorealistic moon mounted on aventurine to track the moon phases, accurate through 125 years and 317 days. It is driven by the in-house cal. 5134 that is based on the ultra-thin cal. 2120, also featuring a central rotor run on rails for more robust build.