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When Stephen McDonnell set out to redesign the perpetual calendar for MB&F, he proposed a system that rethought the entire mechanical basis of the complication. The LM Perpetual uses a “mechanical processor” consisting of a series of superimposed disks.

This revolutionary processor takes the default number of days in the month at 28 — because, logically, all months have at least 28 days — and then adds the extra days as required by each individual month.

This ensures that each month has exactly the right number of days, and removes the possibility of the date jumping incorrectly. An inbuilt safety feature disconnects the quickset pushers during the date changeover, so that even if the pushers are accidentally actuated whilst the date is changing, there is no risk of damage to the movement.

MB&F LM Perpetual EVO Blue

In design, in technique, in spirit, Legacy Machine Perpetual EVO has been an evolution of your story with MB&F.

The LM Perpetual EVO is not a watch for sports. It is a watch for life.

MB&F LM Perpetual EVO Blue

Calendric computation

Conventional perpetual calendars are generally modules comprising the complication, which is fitted on top of an existing movement. The calendar indications are synchronised by a long lever running across the top of the complication and passing through the centre. As the date changes, this long lever transmits information to the appropriate components and mechanisms by moving backwards and forwards.

This traditional system, while beautiful in its interplay of levers and components, is also extremely unwieldy, restricting movement construction in several key ways that would make something like Legacy Machine Perpetual a mechanical impossibility.

MB&F LM Perpetual EVO Blue

Created by Stephen McDonnell and premiered in 2015, the LM Perpetual Engine was — and still is — one of the most innovative perpetual calendar systems to exist in modern watchmaking.

In the traditional system, perpetual calendars assume that, by default, all months have 31 days. At the end of months with fewer than 31 days, the mechanism quickly skips through the superfluous dates before arriving at the 1st of the new month.

Any manipulation or adjustment of the date during the changeover can result in damage to the mechanism, requiring expensive repairs by the manufacturer. The dates can also jump or skip during changeover, negating the whole point of the perpetual calendar in the first place, which is not requiring adjustment for years. Or decades.

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