Audemars Piguet's "Royal Oak Concept Split-Seconds Chronograph GMT Large Date" is a "stunt" that ushered in a new era of split-seconds chronographs.

Audemars Piguet became a manufacture in the early 2000s. By accumulating design know-how, the company is now able to incorporate unique designs into its movements. The company's specialty is symmetrical openwork, but it has now also demonstrated exceptional skill in space-saving. The Royal Oak Concept Split-Seconds Chronograph GMT Large Date, announced in 2023, is a masterpiece that incorporates multiple functions into an automatic watch, an unprecedented feat that minimizes the thickness of the movement.

The donut-shaped rotor makes it possible to implement a natural split-seconds function

　I believe that the degree of perfection of a movement is inversely proportional to its expandability. In other words, the more perfect a movement is, the more difficult it is to add additional functions. A good example is the first Lange 1 from A. Lange & Söhne. The L901 movement it contained was an attractive mechanism, but expanding the baseplate of the compact movement and adding a barrel resulted in wasted space in the movement. However, this was turned around, allowing the Lange 1 to later add various additional mechanisms. This is an extreme example, but it is true that the more space a movement has, the more expandable it is. This is why major manufacturers choose the tourbillon, with its compact gear train, as the base for their complex mechanisms.

　In terms of high level of perfection, Audemars Piguet's Caliber 4401, released in 2019, was an astonishing movement. While enlarging the baseplate diameter and slimming the movement were modern, the large mechanism was packed to the brim with as much functionality as possible. The larger balance wheel increased the moment of inertia to 13 mg/cm2, and the equally large barrel provided a long power reserve of approximately 70 hours. The automatic winding mechanism also featured a highly efficient reverser from MPS, and the reset mechanism was made heavy to accommodate flyback. Today, the standard for chronographs is to reset three heart cams with a single reset hammer. However, the 4401 took advantage of the ample space to feature a "rich" reset mechanism. The 4401 is perhaps the only movement with separate reset hammers and their respective springs for each of the three heart cams.

　While I was very impressed with this movement, I also predicted that it would be difficult to create a more complex model based on it, as it would be impossible to add additional mechanisms to such a large and densely packed mechanism.

　My predictions were completely overturned by the Royal Oak Concept Split-Seconds Chronograph GMT Large Date, released in 23. Adding a large date and GMT to the dial side makes sense, since there is ample space at the 12 o'clock position and in the center on the dial side of the movement. However, adding a split-seconds mechanism to the 4401, which is by no means thin, was unexpected.

　When adding a split-seconds function to an automatic chronograph, a split-seconds module is usually placed under the rotor. However, Audemars Piguet has modified the central rotor to a peripheral, donut-like shape, freeing up space in the center of the movement and embedding the split-seconds mechanism there. It's quite a feat, but if you want to add a split-seconds function without increasing the thickness of an automatic chronograph, this seems like the best solution.

　Lucas Raggi, who oversaw the development of this watch and the Universelle, said, "The development of this watch proceeded in parallel with the Universelle. As a result, the big date and split-seconds mechanisms are common to both." According to Raggi, the rotor of the 4401 was quite thick, with plenty of room around it. He decided to carve out the center and add a split-seconds mechanism. However, a donut-shaped rotor cannot be expected to provide high winding efficiency. Raggi therefore replaced the rotor with one made of platinum, which has a higher specific gravity, and reconfigured it so that it is held in place by 21 ceramic balls. Surprisingly, despite the ceramic balls, the rotor makes almost no noise.

　To make the watch thinner, the isolator that separates the chronograph and the split wheel was omitted. Rudge says that the torque of the mainspring is so strong that an isolator is not necessary.

　The Caliber 4407 adds a GMT, large date, and an astonishing split-seconds function without compromising the high level of perfection of the 4401. I knew that Audemars Piguet excels at symmetry, but their ability to effortlessly pull off such a feat far exceeded my expectations.