What is the Calibre 240 Q?

The Calibre 240 Q is Patek Philippe's ultra-thin automatic perpetual calendar movement, built around a micro-rotor that winds the mainspring through a small rotor recessed into the movement plate. It powers the reference 5327 and was used in the 3940 and 5140.

How does the 5320G differ from the 5327?

The 5327 uses the ultra-thin Calibre 240 Q with a classical dial layout and no center seconds hand. The 5320G uses the Calibre 324 S Q with a center sweep seconds, retrograde date display, and day/month at 12 o'clock. Both are perpetual calendars, but the 5327 is classical and ultra-thin while the 5320G is contemporary and display-forward.

How often does a perpetual calendar need correction?

A perpetual calendar set correctly requires no manual adjustment until the year 2100, when a one-day correction is needed because 2100 is not a leap year despite being divisible by four.

What is a micro-rotor?

A micro-rotor is a self-winding mechanism in which the winding rotor is a small disc recessed into the movement plane rather than a full-sized rotor mounted above the movement bridges. This allows for a thinner overall movement profile. Patek Philippe's Calibre 240 series uses this construction.

Patek Philippe Perpetual Calendar

Q: What was the first perpetual calendar wristwatch?

The Patek Philippe reference 1526, introduced in approximately 1941, is the first serially produced perpetual calendar wristwatch. It predates comparable wristwatch perpetual calendars from any other manufacture.

A perpetual calendar is watchmaking's answer to the irregular structure of the Gregorian year. It knows not just how many days are in each month — 28, 29, 30, or 31 — but sequences through them automatically, including the four-year cycle of leap years. Once correctly set, a perpetual calendar wristwatch requires no manual adjustment until 2100, the century year that is not a leap year despite being divisible by four. Patek Philippe has been producing perpetual calendar wristwatches longer than any other manufacture, beginning with the reference 1526 in approximately 1941, and the complication has remained central to the brand's technical identity through every decade since.

The reference 1526 holds the distinction of being the first serially produced perpetual calendar wristwatch. Introduced in approximately 1941, it placed the complication — which had existed in pocket watches for over a century — into the format that would define the twentieth century's approach to fine timekeeping. The 1526 was powered by a manually wound movement and displayed the perpetual calendar's outputs across a dial arrangement that would establish the visual grammar used by Patek for decades afterward: separate apertures or subdials for the day, date, month, and moon phase.

The reference 3940, introduced in 1985, defined the perpetual calendar wristwatch for a full generation of collectors. It was powered by the Calibre 240 Q — a self-winding movement built around Patek's celebrated micro-rotor, which winds the mainspring through a small rotor recessed into the movement plane rather than a full-sized rotor spinning above it. The result is a thinner movement profile that allowed the 3940 to achieve dimensions appropriate to a dress watch despite the mechanical complexity of a perpetual calendar.

The Calibre 240 Q remains one of Patek's most important movements. The micro-rotor design compresses the movement to a total thickness that few manually wound perpetual calibres can match, and the mechanism's reliability over decades of service established it as the reference standard for automatic perpetual calendar movements. The 3940's dial layout — day and month in windows at 12 o'clock, date indicated by a large hand pointing to a peripheral scale, moon phase at 6 o'clock — became the template that subsequent references would modify but not fundamentally redesign.

The reference 5140, introduced in 2006, carried the Calibre 240 Q forward into a 38.5mm case with an exhibition caseback that revealed the micro-rotor's elegance. It was the direct evolution of the 3940: same movement architecture, more refined presentation, and an overall package that positioned the perpetual calendar as an ultra-thin dress watch rather than a technical showpiece. The 5140 was discontinued and replaced by the 5327, but it occupies an important position in the transition from the 3940's generation to the current catalogue.

The 5327, introduced in 2016, is the current flagship perpetual calendar built on the Calibre 240 Q platform. It uses Breguet Arabic numerals on its dial — a choice that references the historical typographies of eighteenth- and nineteenth-century watchmaking — and maintains the classical case proportions established by the 5140. The 5327 is, by explicit design philosophy, the heir to the 3940's tradition: a perpetual calendar that presents the complication with maximum elegance and minimum case bulk.

The 5320G's display is organized around a day and month indication at 12 o'clock — both in the same window, separated by a vertical marker — with a retrograde date display using a hand that sweeps across a sector before snapping back at month-end. This is a more visually animated approach to the perpetual calendar than the classical layout, and it attracted significant collector attention at launch, particularly in the salmon dial variant (5320G-011), which combined the retrograde display with a warm pink-toned dial in white gold.

The perpetual calendar's ability to track irregular month lengths automatically is achieved through a programmable cam or lever system that encodes the calendar year's structure. A 48-month cam — one full rotation over four years — carries the information needed to advance the date display by the correct amount at each month-end, accounting for the 28, 29, 30, and 31-day months in sequence. The February 29 position on the cam is active only once every four years, handling the leap year automatically.