IWC's Lorenz Brunner about the Portugieser Eternal Calendar

Behind the Scenes: IWC’s Lorenz Brunner on the Birth of the Portugieser Eternal Calendar

In 2024, the Schaffhausen-based maison is setting its sights on the future with its first secular perpetual calendar watch.

By Rhonda Riche

One of the best conversations we had at Watches and Wonders 2024 was with Lorenz Brunner, the man responsible for IWC’s Research and Innovation department.

Brunner’s position is unique in that he heads a team responsible for creating state-of-the-art materials – such as Ceratanium – and updating venerable complications in the name of accuracy and durability.

This year, however, Brunner and his team’s work was focused on a much more distant future with the Portugieser Eternal Calendar – a watch featuring the rare secular calendar complication, which is so advanced that it automatically accounts for exceptional non-leap year years (2100, 2200, etc.) in the Gregorian calendar by skipping three leap years over 400 years.

Moreover, its moonphase display is so precise that it will only deviate by one day after 45 million years.


“If we’re being honest,” Brunner told Watchonista, “I have the best job at IWC. We have such a variety of projects that we are working on, and it’s such a pleasure to combine the material and the technological.”

Not that it’s his first time at the rodeo. Brunner was behind 2021’s Big Pilot’s Watch Shock Absorber XPL (Ref. IW357201), which was a perpetual calendar with a super lightweight, all-Ceratanium case and bracelet.

Still, Brunner admitted that the innovation team rarely gets to become involved with the kind of technical challenges the Portugieser Eternal Calendar proposed. Very few watchmakers do. Here’s how the plan came together.

“Once someone comes up with an idea like making a secular calendar, the first step for the team is to make a proof of concept – an investigation that such a proposition was even feasible,” explained Brunner. The team accepted the challenge heartily.

“It’s so complex to create an accurate moonphase,” added Brunner. To get it right, the team had to go back to basics – not just for the mechanism but to understand time itself. “We talked to astrophysicists and studied astronomical almanacs.”

The more the IWC team grasped the assignment, the more enthusiastic they got about the project. “From the prototype, it was really like Christmas,” remembered Brunner. After computing simulations for more than 22 trillion combinations of wheels, they devised a new moonphase reduction gear with three intermediate wheels.

The Final Frontier

As we spoke about the birth of the Eternal Calendar, I noticed that Brunner’s enthusiasm for the project was still strong, even after years of trial and error, disappointment and elation. Moreover, as watch fans, we were both sitting on the edge of our seats, equally excited to delve into the minutiae of the Eternal Calendar’s development.

A big part of the story is that, when it came to realizing this perpetual calendar project, the team’s expertise in materials proved just as important as the engineering.

A lot is going on with this watch on the inside, but it all makes sense on the outside. “What I like are the visible elements,” Brunner said. For example, the minimalist double Moon display of the Portugieser Eternal Calendar will theoretically only deviate from the moon’s actual orbit by one day after running for 45,000,000 years (we joked about setting up an order of caretakers to watch over the watch to protect and monitor its progress).

Luckily, IWC’s history of innovation in difficult-to-manipulate materials, such as titanium and ceramic, made an excellent foundation for creating the Eternal Calendar’s a layered, transparent dial because, aesthetically, it is far more pleasant to look at than a skeletonized piece. In fact, it looks as if all of the elements on the Eternal Calendar’s dial are floating in a calm sky.

Bringing all the elements together, added Brunner, was not as easy as you would think: “We would do these nice renderings, but when you replaced a metal part with a ceramic one, it would seem impossible. It took maybe five years to figure out how to produce a transparent dial.”

“In innovation, you need to learn every day,” continued Brunner. “Because we do everything in-house – the machining and grinding – we also had to challenge production. We could not have made this watch 15, 16 years ago.”

While the Portugieser Eternal Calendar is out in the world, Brunner is still looking forward to the future. After five years of this project, the Innovation team is just as excited to start working on new, out-of-this-world projects. We asked for a teaser, but he could only hint that it had to do with “the dimensions of tomorrow.”

For more information about the Portugieser Eternal Calendar, visit IWC’s website.

(Photography by Pierre Vogel)

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