Over the last decade, there have been rapid developments in all aspects of ultra-thin watchmaking from self-winding movements to high complications, with Piaget and Bvlgari locked in a perpetual slimming contest to shave hundredths of a millimetre off each other. Back in March, Bulgari had its nose in front with the launch of the Octo Finissimo Ultra that clocked in at a staggering 1.8mm, usurping the Piaget Altiplano Ultimate Concept, which had held the record for the world’s thinnest mechanical watch since 2018, by 0.2mm. But now Richard Mille has arrived completely out of left field with the RM UP-01 Ferrari, stealing the title with the watch’s barely-there height of 1.75mm. And to add insult to injury, it did so with a conventionally solid construction, boasting a full main plate separate from the case.
The rapid pace at which records are set and broken today has somewhat attenuated the fact that making an especially flat mechanism was and still is a sure sign of engineering prowess. Along with the fact that all aspects of a watch – from case and strap to the crown and keyless works to the mainspring and balance – have to be critically rethought, it also gets increasingly difficult to deliver reliable performance as height plummets because slighter parts are necessarily weaker. There is, thus, no room for error in manufacturing and assembly, and chronometric potential is by nature compromised; there is no headroom for overcoils, for instance. What makes the category more interesting in recent times is that amidst the quest for thinness, there is also an intelligible fight for the smallest performance gains.
In fact, all three contenders can be said to represent a new generation of ultra-thin watches where performance takes greater precedence than ever before. All of them, for instance, operate at 4Hz, as opposed to the more common 3Hz frequency practiced in this sector of watchmaking as a consequence of a thinner, weaker mainspring as well as to preserve power reserve. Additionally, the use of unconventional materials such as titanium and M64BC offer higher structural rigidity while simultaneously reducing the weight of the watch. Above and beyond all records, each watch has introduced its own unique and at times highly imaginative solutions to saving precious micro-millimetres, making technical comparisons, apart from sheer numbers, far from straightforward.
Piaget Altiplano Ultimate Concept
Stemming from four years of research and development, the Piaget Altiplano Ultimate Concept first saw the light of day in 2018 before arriving on the production line in 2020. Coming in at a staggering 2mm in height, the AUC relied on some well-established solutions such as having the case back milled to accommodate the moving parts and designing an offset dial with its motion works driven by a separate train so all components can be fitted on a single plane. Both solutions were first adopted in the Piaget 900P, which, at 3.65 mm high, stood as the thinnest mechanical watch at the time of its launch in 2013.
To put things into perspective, a conventional central-seconds watch has its fourth and second wheels located on the same axis with the motion works sitting above the latter, carrying the hands one on top of the other. But to reduce thickness caused by all the overlapping components, all three gears have to be spread out on the horizontal plane, with the barrel driving the motion works via an auxiliary train highlighted in blue in the diagram below. And to further suppress its height, the hour hand is printed on an hour rotating disc. However, at this level of wafer-thin watchmaking, more components had to be jettisoned and others radically redesigned, beginning with the crown and the keyless works. In fact, these components mark the greatest departures from ultra-thin watches that came before.
A conventional crown that accommodates a case as thin as a nickel would be impossible to handle, hence the crown takes a rectangular form and is seamlessly recessed into the case band. This preserves the symmetry of the case while protecting the crown from impacts. But an inevitable downside is that it is still not big enough to be operated with bare fingers, thus requiring a motorized tool for both winding and setting. More impressive are the modifications in the keyless works, which conventionally are made up of a winding stem, clutch, winding and sliding pinion which collectively take up both vertical and horizontal space. Piaget’s ingenious solution is a worm screw, which it dubs the “infinite screw”. Its spiral threads enable it to engage and drive a gear laterally on the same plane, significantly reducing the footprint.
Additionally, the barrel has an open design revealing its state of wind in a “hanging” construction. However, it is supported on its periphery by ceramic ball bearings in addition to being supported on its bottom pivot. In the same vein, the balance assembly – its hairspring, staff, cock, shock absorber jewel cap – which determines the height of every movement, had to be rethought. For the first time in a watch, the balance is not secured in place by a bridge or a cock. Instead, the shaft of the balance is supported on ball bearings integrated in the main plate. This reduces the height of the movement while eliminating the need for shock absorbers. And as a result of removing the balance cock, the hairspring had to be attached to a circular bridge screwed to the main plate, hence is located under the balance wheel. Consequently, with such a design, the balance had to be free-sprung.
The gears in the movement measure a mere 0.12mm and the sapphire crystal 0.2mm, both barely thicker than a human hair. As a result, the crystal is prone to bending and touching the moving parts, which will impede function. Thus, there is a narrow bridge surrounding the apertures to prevent the crystal from reaching the depth of the components. Lastly, the case is made of M64BC, a cobalt based alloy, for greater rigidity. This is crucial as it retains the gears and pivots, and at the same time, has a wide diameter of 41mm while being wafer-thin, making it prone to slight distortion when worn too tightly.
Thanks to the numerous unusual solutions, the Piaget Altiplano Ultimate Concept went unassailed for three years.
Bvlgari Octo Finissimo Ultra
The usurper was none other than Bvlgari. Having set numerous records in ultra-thin complications, creating the world’s thinnest mechanical watch was the final notch on its belt. With the 1.8mm Octo Finissimo Ultra this year, it had trumped the world champion by 0.2mm – a generous margin as far as this sector goes. Conceived in collaboration with Concepto, the Ultra matches the AUC in its fundamental construction, namely having the base plate integrated into the case back and driving the motion works via a secondary train, but from there it diverges. In fact, most prominently, it features a regulator-style display with the hours, minutes and seconds split into three sub-dials. This means that the motion works are further divided, necessitating more wheels but less overlapping of which.
More drastically, in place of a conventional crown, it features two planar crowns set into the case back – one on the right for winding the barrel and one on the left for time-setting. This solution effectively eliminates the need for the keyless works and its clutch, saving the vertical and horizontal space required for all its perpendicular components. But consequently, a differential had to be used to separate the gears for time-setting from the wheel train. A unidirectional winding click, similar to that for winding the barrel, had to be used to prevent the gear train from unwinding. This planar configuration also enables the crowns to be wound by fingertips.
The differential is powered by an additional wheel in the gear train driven directly by the barrel. There are thus five wheels in the wheel train inclusive of the barrel, which results in a counter-clockwise rotation of the fifth wheel, like in the Piaget AUC. While the AUC does away with a seconds indication completely, the Ultra has its seconds chapter ring directly printed on the fifth wheel and requires a separate pointer printed on the bridge below so the seconds can be read more intuitively as it is rotating backwards.
The volume of the movement has been thoroughly optimized, with the barrel occupying half of the movement’s diameter, enabling it to deliver a respectable power reserve of 50 hours on a 4Hz escapement. It has a floating or hanging construction, with its arbour supported only on its bottom end, and is topped by a ratchet wheel, on which a QR code providing access to an NFT artwork is engraved.
Most significantly, the balance wheel is housed in a two-part bridge – a three-arm upper bridge with an integrated stud holder and a circular plate below – that is screwed to the main plate. This construction allows the entire balance assembly unit to be conveniently removed during servicing. At the same time, the bridge also acts as a shock absorber, protecting the core of the watch in an event of an impact, eliminating the need for a conventional shock protection system, which only adds height. The escapement has also been redesigned to minimise height, doing away with a safety roller and guard pin.
While the bracelet, bezel and case band of the Ultra are made of titanium, the case back accommodating the moving parts is made of tungsten carbide, a metal that is even harder than titanium. The sapphire crystal measures just 0.3mm thick, making it prone to flexing when pushed, potentially touching the hands. Thus, a pair of silicon bumpers are installed under the dial to prevent the crystal from reaching the components.
Beyond claiming the title with a full slate of creative strategies, the Ultra is a masterclass in reconciling user practicality – having a seconds sub-dial, ability to be wound by hand, impressive power reserve, a modest, 40mm case diameter – with slimness, and doing so in accordance with an inimitable house style.
Richard Mille RM UP-01 Ferrari
After a mere four months into its reign, the Ultra has already been outdone by a new entrant in ultra-thin mechanics. At a mind-blogging 1.75mm high, the RM UP-01 Ferrari is 0.05mm or almost three percent thinner. In contrast to its predecessors, this feat was achieved with a full and separate main plate, measuring 1.18mm, fitted in a titanium case.
While it relies on some textbook solutions such as distributing the gears across a single plane, the painfully thin movement has been engineered to withstand accelerations of over 5,000 Gs, which is a hundred times more than a car crash. The movement is made of titanium which offers substantial rigidity. In contrast to its predecessors, the moving parts in the movement is further fortified by an upper titanium plate as well as a case back. Held together by 13 screws, the top plate sits flush with the case back with the main plate sandwiched in between.
The upper plate displays the offset dial, the balance wheel as well as a pair of apertures on the left. Like Ultra and the AUC, the winding stem, which occupies a minimum height of 1.5mm, had to be deep-sixed. Thus, the watch does not have a conventional crown. Instead, it features a function selector in the top left aperture, allowing the user to switch between winding and setting while both of these functions are carried out via a second port in the aperture on the bottom left. This makes setting the time or winding the mainspring each time a two-step procedure, which is operated by a special key.
The calibre benefits from its particularly wide dimensions. All the components are spread out comfortably with minimal stacking. The motion works are driven by the barrel via an auxiliary train, and in turn, the minute and hour wheels drive a pair of discs respectively for the time display. The barrel is extremely thin and is fitted with an exceptionally fine mainspring. Thus, the floating barrel had to be secured to the base plate by rollers. The winding wheels as well as auxiliary train occupies the right expanse of the movement while the gear train is relegated to the left.
Like the rest of the watch, the balance is made of titanium with six integrated slots for the adjustable weights. Its design is similar to the one in the new Audemars Piguet cal. 7121 – both courtesy of the technical research powerhouse APRP. It has a wide and completely flat rim to minimise air resistance. Similarly, the hairspring is attached to a stud holder affixed to the main plate. And the last bit of innovation lies in the escapement, which has been modified to omit the safety roller and guard pin, allowing the escapement assembly to be thinner.
While ultra-thin watchmaking is an ongoing battleground with virtually no end in sight, the RM UP-01’s robustness and shock resistance, particularly in this sector of micromechanics, represent a different level of achievement that is tough to beat, at least not any time soon.