The Ref 5212A-001 indicates the week using what Patek Philippe calls a hammer-shaped hand, with the head of the “hammer” coloured red for added legibility and aesthetic enhancement. When creating the watch, Patek Philippe used the ISO 8601 standard, an international guideline that applies to representations and formats of dates in the Gregorian calendar—the one most commonly used around the world. Under the ISO 8601, all weeks begin on a Monday and the first week of the year is the one in which January 4 occurs. And while we all know that a year contains 52 weeks, the eagle-eyed watch buff will notice that the indications on the Ref 5212A-001 go up to 53 weeks. It is true that some years do indeed have 53 weeks—if the year starts on or after a Thursday, or if it is a leap year starting on or after a Wednesday. The next 53-week year will be the year 2020, which means the new weekly calendar comes well in time for its arrival.

The Ref 5212A-001 has a completely new self-winding movement, the calibre 26-330 S C J SE, which is based on the classic calibre 324 that sits within many of Patek Philippe’s other calendar watches. The new calibre has a new semi-integrated mechanism for the weekly calendar function. In addition to the week, date, and day indication functions, the movement also has a stop seconds mechanism that allows for greater precision when the crown is pulled out for time-setting, as well as an improved self-winding mechanism.
 

The most interesting part of the Ref 5212A-001, however, is its design. According to some reports, it was inspired by a one-of-a-kind extra large historical reference from 1955, the Ref. 2512/1, which went under the hammer at Sotheby’s for US$962,500 in 2012. Perhaps, it is not mere coincidence that the reference name of the new watch is an anagram of the Ref. 2512. There are subtle design parallels between the two, though limited mostly to the case—both references have two-tiered lugs and a two-tiered case, as well as a boxed sapphire crystal. Unlike the yellow gold Ref 2512/1, however, the case of the Ref 5212A-001 is made from stainless steel—it is the only Calatrava in Patek Philippe’s regular collection to be made in steel. The material is typically reserved for sporty Nautiluses and limited editions.

All of the aforementioned elements have been crafted and engineered to perfection—or as close to perfection as human hands can accomplish. With handiwork, every piece is unique and that is what makes the Weekly Calendar Ref 5212A-001 so special. And you can see it on the first look at the watch. Each of the letters and numbers on the dial (aside from the usual Patek Philippe Geneva logo, the Swiss-made branding and the date aperture) is written by hand—the hand of a designer in the manufacture, to be more precise though Patek Philippe has kept the name of the said designer a secret.

(Related: How The Patek Philippe Nautilus Became An Icon)

The handwritten numerals and letters add a touch of quirkiness that has never quite been seen before in Patek Philippe’s watches—this is the first time it has ever used hand-lettering in its dial design. Unlike typography, each handwritten letter and number is just slightly different. The imperfection of the writing, however, is what makes the Ref 5212A-001 so unusual—it presents a touch of whimsy that is very rare in Patek Philippe’s oeuvre.

(Related: 4 Beautifully Handcrafted Patek Philippe Watches Suited For Heirloom Status)

Perhaps this is the watchmaker’s attempt to introduce an element of informality in its round dress watches, in a way that is different from that conveyed by the sportiness of the Nautilus or Aquanaut. More importantly, it serves as an indication of how it is created by the skilled hands of its artisans, who put their heart and soul into its making—the very quality that makes it truly one-of-a-kind.