MB&F’s Most Revolutionary Perpetual Calendar LM Perpetual Gets A Gem-Set Glow Up

Some watches are celebrated for their aesthetics. Others are revered for their mechanics. The MB&F Legacy Machine Perpetual has always excelled at both. Since its debut in 2015, the watch has challenged long-held conventions surrounding one of watchmaking’s most traditional complications while presenting its intricate mechanics in a manner few perpetual calendars have dared attempt. Now, more than a decade later, MB&F introduces a colourful new interpretation of this modern icon with the launch of the LM Perpetual Chromatic Editions three highly exclusive references that marry groundbreaking horology with the brilliance of coloured gemstones. Limited to just eight pieces each, the new Chromatic Editions demonstrate that technical innovation and high jewellery craftsmanship can coexist beautifully, transforming one of MB&F’s most celebrated creations into something even more expressive.

A Brilliant New Look

The LM Perpetual Chromatic Editions introduce colour in a way that feels both bold and refined. The collection comprises three distinct versions, each framed by a bezel set with 48 baguette-cut gemstones arranged in a continuous circle around the dial. Two of the editions are crafted in 18K white gold and feature bezels set with either deep blue sapphires or rich purple sapphires. The third is housed in an 18K red gold case and adorned with a bezel set with vivid red rubies, creating a particularly striking visual presence.

Each gemstone is individually hand-set by the skilled artisans of Geneva-based STG Creation, a long-standing Friend of MB&F renowned for its expertise in gem setting. Impressively, this dazzling addition has been achieved without increasing the diameter of the case, ensuring that the elegant proportions of the Legacy Machine remain perfectly intact. The colour story extends beyond the bezel. The hands have been specially treated to harmonise with each model’s gemstone palette. Purple PVD-treated hands complement the sapphire-purple edition, blue PVD hands accentuate the blue sapphire version, while the ruby edition features 5N PVD-treated hands that echo the warmth of the red gold case. The result is a watch that feels simultaneously contemporary and timeless, with the gemstones acting as a radiant frame for the mechanical masterpiece beneath.

Why Traditional Perpetual Calendars Needed Reinvention

Perpetual calendars are among watchmaking's most revered complications. Their purpose is deceptively complex: automatically accounting for months of varying lengths, including leap years, without requiring manual adjustment for decades. Yet traditional perpetual calendars often come with compromises.

Most rely on a module fitted atop an existing movement. Their operation is controlled by a long lever known as the grand levier, which coordinates the calendar indications as the date changes. This architecture creates significant design limitations, requiring a largely closed dial and restricting the placement of components.

More importantly, conventional perpetual calendars assume every month contains 31 days. At the end of shorter months, the mechanism rapidly skips through the unnecessary dates before arriving at the first day of the next month. During these transitions, the movement can be vulnerable to damage if adjusted incorrectly. As Büsser famously remarked: "I call perpetual calendars boomerang watches because they come back for repair so often. The mechanisms jam, block, break or jump days when they shouldn't."

The Mechanical Processor

Stephen McDonnell’s answer was to discard the traditional system entirely. Instead of using the conventional grand levier architecture, he developed what MB&F calls a mechanical processor a revolutionary system composed of a series of superimposed discs. The logic is elegantly simple. Rather than assuming a 31-day month, the processor assumes a default month of 28 days, since every month contains at least 28 days. Additional days are then mechanically added only when required.

This means each month always contains precisely the correct number of days. There is no need to skip through redundant dates and therefore no risk of incorrect date jumps. The processor also introduces several practical benefits. The leap year can be adjusted using a dedicated quick-set pusher rather than requiring the user to cycle through up to 47 months, as is often necessary on traditional perpetual calendars. Meanwhile, the quick-set pushers automatically disengage during date changeovers, eliminating the possibility of accidental damage. The result is a perpetual calendar designed for real-world reliability without sacrificing complexity.

Opening Up the Perpetual Calendar

Eliminating the grand levier had another important consequence: it freed the centre of the movement. This seemingly technical change opened entirely new possibilities for the watch’s design. Without the large lever passing through the middle of the movement, MB&F could create a perpetual calendar unlike any other. The calendar mechanism is displayed openly on the dial side, allowing every aspect of its operation to be appreciated. Skeletonised subdials are positioned around the dial and appear to float above the movement without visible supports.

This illusion is achieved through an innovative hidden-stud construction developed specifically for the LM Perpetual. Such an arrangement would be impossible in a traditional perpetual calendar because the supporting structures would obstruct the movement of the grand levier. The display layout remains remarkably intuitive despite the complexity beneath. Hours and minutes are positioned at 12 o’clock beneath the balance wheel arches, while the day indication sits at 3 o’clock. The power reserve is displayed at 4 o’clock, the month at 6 o’clock, the retrograde leap-year indicator at 7 o’clock and the date at 9 o’clock.

Balance Above, Escapement Below

Perhaps the most visually captivating element of the LM Perpetual is the oversized balance wheel suspended high above the movement. Hovering beneath MB&F’s signature twin arches, the balance dominates the dial and creates the three-dimensional architecture that defines the Legacy Machine collection.

Technically, however, its placement presented a significant challenge. The balance is connected to the escapement on the reverse side of the movement through what is believed to be the world’s longest balance staff, ensuring both reliability and visual drama. Turn the watch over and the spectacle continues. The display back reveals the escapement in motion alongside exquisitely hand-finished bridges and plates that showcase traditional haute horlogerie finishing at its finest.

A Rare New Chapter

The LM Perpetual Chromatic Editions demonstrate just how versatile this groundbreaking platform has become. By pairing Stephen McDonnell’s revolutionary perpetual calendar with meticulously hand-set sapphires and rubies, MB&F has created watches that celebrate both technical ingenuity and artistic expression. Limited to only eight examples each, these new editions are among the rarest Legacy Machine Perpetuals ever produced. Yet beyond their exclusivity, they represent something more meaningful: proof that even one of watchmaking’s oldest and most traditional complications can continue to evolve, surprise and delight. With the LM Perpetual Chromatic Editions, MB&F once again reminds us that true innovation is not only about solving technical problems. Sometimes, it is also about adding a little more colour to the story.