Piaget has a long and distinguished record in making very thin watches and has repeatedly broken records in this category. The Altiplano 900P, launched in 2014, is just 3.65mm thick, which by some fortuitous number magic happens to be the average elevation in kilometres of the Altiplano, an enormous high plain in Bolivia and Peru. The designation “900P” is a nod towards the 9P, produced in 1957. This had a manual-wound mechanical movement that was a record-breaking 2mm thick. How thick is the Altiplano movement? It’s impossible to say: in the traditional sense, it doesn’t have one. But let’s first take a view of the watch as a whole.

Piaget
Piaget

It’s certainly an interesting looking piece. The eccentric dial is displaced towards 10 o’clock, with the winding gears, wheel train and balance forming a crescent in the vacated space. The watch is available in a number of formats. I rather think it’s more attractive in the white gold versions with the black sunburst bridges than the yellow gold with silver, but that’s a matter of opinion. There are options with a diamond set bezel and also a jewellery variant with 304 diamonds totalling 4.71 carats. Accommodating this bling adds 2mm to the overall thickness; presumably moving us up into the foothills of the Andes. From the side, the standard models almost disappear from view, appearing no thicker than the watchstrap at the horns.

Piaget
Piaget

Thinking outside the sandwich

Conventional watches are made up of separate units put together rather like a sandwich. The movement is the filling, and the case and crystal are the bread. Actually it’s more of a club sandwich, the dial and hands making an additional layer. Thin movements have always been regarded as one of watchmaking’s major challenges, but using the sandwich system, no matter how thin you manage to make the movement, the addition of these extra layers will thicken the watch by two or three fold. The 2010 Altiplano, made in this way, was 6mm thick.

Piaget’s triumph with the latest version was to think outside the box, or rather the sandwich, by making the case-back act as the mainplate itself. An exploded view of the Altiplano 900P illustrates its construction. Far from the simple container you’d normally find, the case-back at the bottom is a complex structure machined to miniscule tolerances from a block of special hard gold alloy.

Piaget
Piaget

All that complexity is squeezed into a shape less than 2mm deep, about half the thickness of the watch. The bezel, near the top of the picture, makes up the other half and when they are clamped together by the screws around the periphery of the case-back we have a robustobject, despite its slenderness. Starting with a block of metal and removing only enough to leave space for the mobile components provides a strong structure that resists distortion, one of the many hazards afflicting ultra-thin watches.

In making the 900P, Piaget was able to benefit not just from its established expertise in thin watchmaking, but from the fact that it is one of few brands with facilities both for movement making and case making. Collaborative work from these two elements has resulted in a construction that effectively eliminates one layer of the aforementioned sandwich.

Moreover, the filling is more of a buffet: the courses are distributed laterally rather than being piled together. Looking at the front view of the 900P and moving clockwise from the crown, we see the train of normally hidden winding wheels leading to the click wheel (the larger one with the curved spokes). This sits on top of the mainspring barrel, together with the first wheel of the gear train.

Piaget
Piaget

Continuing around we see the second, third, fourth and escape wheels and finally the balance, which is partially accommodated by a cut out in the chapter ring.

This watch lets it all hang out and provides a good introduction to horology. The lucky owner will enjoy educating his friends, if he provides them with loupes. As he winds the crown they’ll see the winding wheels turn, the click wheel and its ratchet operate and the wheels of the gear train turning progressively faster as the escapement kicks the balance into life.

Transfer season

Eagle eyed experts will notice something extra: the jewel hole just inside the chapter ring a 6 o’clock. This houses the pivot for an extra wheel, which is peculiar to this this layout. You can see some of its teeth just below the cut-out in the chapter ring beneath the balance.

Piaget
Piaget

This is a transfer wheel, helping to move time to the centre of the dial: the second wheel in the gear train, which turns once an hour and is normally in the centre of the watch, is in this case at the periphery. The additional transfer wheel is needed to drive the cannon pinion (see glossary box). Squeezed into the same space as the rest of the gear train, the transfer wheel is just 0.12mm, not much thicker than a human hair.

Piaget has also removed height from the mainspring barrel. Most of the wheel train, from the second wheel to the balance, is assembled in the conventional way: the arbors – vertical shafts on which the wheels turn – have pivots at both ends and they run in jewelled bearings set between a plate and a bridge. But the spring barrel is different: it’s called a “hanging barrel”. Instead of having a bearing at top and bottom it is suspended from a single bearing at one end below the click wheel, reducing the vertical space required.

Piaget
Piaget

The winding wheels are also supported from one side and run on ball races. These are an unusual addition, but help negate the extra winding effort that a watch with such tiny winding wheels, not to mention a necessarily small crown, would otherwise require. For a bit of extra watch knowledge, note that two of the screws securing winding wheels have triple slots in their heads. This is to warn the watchmaker that they have left handed threads. The wheels that these screws secure turn counter-clockwise and would have a tendency to undo conventional screws.

Piaget
Piaget
Piaget
Piaget

The Altiplano 900P has one more trick up its sleeve. The dial and hands are slightly recessed with respect to the surrounding bridges. If there is any excessive pressure on the crystal it will be supported by the bridges rather than obstruct the turning of the hands – something on which Piaget has a patent pending. This watch may look delicate but it’s actually quite tough.

Going super-thin

Audemars Piguet Tourbillon 1986
Audemars Piguet

While the search for ever thinner wristwatches has been going on since the 1950s, the idea of using the case-back to house some or all of the components is somewhat newer, but not entirely novel. In 1979 Concord’s quartz-powered Delirium, just 1.98mm thick, employed the case-back as the mainplate, while a few years later the original Swatch watch was based on a precision moulded plastic case onto which the components are mounted. Remarkably, in 1986 Audemars Piguet produced a self-winding tourbillon wristwatch (pictured above) just 4.8mm thick, with the wheel train of its Calibre 2870 movement running on jewels pressed into the case-back.

Find out more about the Piaget Altiplano 900P here