Dang, I just submitted my Christmas list to my kids yesterday, I wonder if they’d mind if I snuck the new MB&F Legacy Machine Perpetual on there. As if. For this latest masterpiece in the Legacy series, MB&F commissioned and encouraged Irish independent watchmaker Stephen McDonnell to sit down with a blank sheet of paper and completely reinvent the most traditional of horological complications: the perpetual calendar. The result is Legacy Machine Perpetual, displaying a visually alluring in-house movement developed by McDonnell from the ground up to eliminate the drawbacks of conventional perpetual calendars.

LM Perpetual features a fully integrated 581-component caliber with no module, no base movement, and with a brand new system for calculating the number of days in each month. It reinterprets the perpetual calendar by placing the full complication on dial-free display underneath a suspended balance.

Renowned as one of the great traditional complications, traditional perpetual calendars do have a few drawbacks: dates can skip; they are relatively easy to damage if adjusted while the date is changing; and the complications are usually compromises of modules powered by base movements.

The fully integrated, purpose-built movement of Legacy Machine Perpetual has been designed from scratch for trouble-free use: so there’s no more skipping dates or jamming gears, and the adjuster pushers automatically deactivate when the calendar changes.

Traditional perpetual calendar mechanisms use a 31-day month as the default and essentially “delete” superfluous dates for the months with fewer days. They do this by fast-forwarding through the redundant dates during changeover. So for example, a traditional perpetual calendar changing from February 28 to March 1, scrolls quickly through the 29th, 30th and 31st so as to arrive at the 1st.

LM Perpetual turns the traditional perpetual calendar system on its head by using a “mechanical processor” instead of the conventional space-consuming grand levier (big lever) system architecture. The mechanical processor works on a default 28-day month and adds extra days as required. This means that each month always has the exact number of days required; there is no fast-forwarding or skipping redundant days. And while the leap year can only be set on traditional perpetual calendars by scrolling through up to 47 months, LM Perpetual has a dedicated quickset pusher to adjust the year. Using a planetary cam, the mechanical processor enables quick setting of the year so that it displays correctly in the four-year leap year cycle, whereas traditional perpetual calendar mechanisms require the user to scroll through up to 47 months to arrive at the right month and year.

With its open dial revealing the full complication and suspended balance, the harmonious mechanical beauty of LM Perpetual is certainly a show stopper. And the eye-catching balance hovering on high is connected to the escapement on the back of the movement by what is likely to be the world’s longest balance staff.

Using an innovative system developed especially for Legacy Machine Perpetual, the subdials appear to “float” above the movement with no visible attachments. The skeletonized subdials rest on hidden studs, which is technically impossible with traditional perpetual calendar mechanisms because they would block the movement of the grand levier.

At 12 o’clock the hours and minutes are nestled between the elegant arches of the balance; day of the week at 3 o’clock, power reserve indicator at 4 o’clock, month at 6 o’clock, retrograde leap year indicator at 7 o’clock, and date at 9 o’clock. Complexity simplified with integrity and beauty.

Legacy Machine Perpetual launches with a limited edition of just 25 pieces in 18K 5N+ red gold and 25 pieces in platinum 950.

About Stephen McDonnell

Stephen McDonnell was born in Belfast, Northern Ireland in 1972.

After completing a degree in theology at Oxford University, McDonnell returned to Belfast and gradually fell into repairing clocks for a number of watch and clock shops. This led to the realisation that watchmaking might well be a career after all. After completing a one-week Rolex course − until then his experience had been virtually exclusively with clocks − McDonnell moved to Neuchâtel, Switzerland in 2001 to do a six-month course at WOSTEP (Watchmakers of Switzerland Training and Educational Program). Upon completion, he was offered an instructor position at WOSTEP, which he held until 2007 when he decided to set up as an independent watchmaker. He likes to control all aspects of the development process from conception through to 3D design, construction, the creation of technical plans, and prototyping.



Fully integrated perpetual calendar developed for MB&F by Stephen McDonnell, featuring dial-side complication and mechanical processor system architecture with inbuilt safety mechanism. Manual winding with double mainspring barrels. Bespoke 14mm balance wheel with traditional regulating screws visible on top of the movement. Superlative hand finishing throughout respecting 19th century style; internal bevel angles highlighting hand craft; polished bevels; Geneva waves; hand-made engravings

Power reserve: 72 hours

Balance frequency: 18,000bph / 2.5Hz

Number of components: 581

Number of jewels: 41


Hours, minutes, day, date, month, retrograde leap year and power reserve indicators


Material: launch editions in 18K 5N+ red gold or platinum 950

Dimensions: 44 mm x 17.5 mm

Number of components: 69 components

Water resistance: 30 m / 90’ / 3 atm


Sapphire crystals on top and display back treated with anti-reflective coating on both faces


Black or dark brown hand-stitched alligator strap with gold / platinum folding buckle matching case material

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