In the panoply of Patek Philippe complications, the split-seconds chronograph is true royalty. Launched at Baselworld 2015, the exquisite reference 5370 continues an haute horlogerie story that stretches back to 1923.

After the sturm und drang, and indeed clang, of Patek Philippe’s 175th anniversary watches – most notably the baroque excesses of the Grandmaster Chime everything-repeater, plus an elaborately engraved chiming jump hour, a curious one-minute chronograph with multiple scales, and a showy world time/moon phase – it’s arguably a relief to encounter something aimed squarely at the Patek purist.

For that is what reference 5370, a gorgeous split-seconds chronograph in a sleekly curving case and with a dial in inkiest black enamel, undoubtedly is. It’s one of the most beautiful watches of Baselworld 2015, the cover watch for our new issue (out today!) and will have collectors frothing right around the world.

Notable aesthetic elements, beyond that sensational hand-enameled dial: an intriguing new platinum case design with a slighly hollowed-out flanks and scooped bezel; Breguet numerals, and feuille hands carrying thin slivers of lume.

Patek Philippe 5370
Gary Smith

At 41mm it’s pretty large for Patek Philippe, andmuch larger than the other pure split-seconds chrono in the Patek Philippe armoury the 33mm 5959 monopusher.

Given the spectacular prices the brand’s split-seconds pieces command – this one is priced around £180,000, which actually makes it entry-level for the complication (at Patek) for reasons we’ll explain – not to mention their rareness, for most Patek devotees these will remain a pipedream. But as emblems of the brand’s peculiar mystique, the split seconds sits alongside minute repeaters and perpetual calendar chronographs – and possibly a little bit above – as a defining Patek speciality.

The one that started it all

We were reminded of that point last June when Sotheby’s New York auctioned off one of the most celebrated historic Patek Philippe watches of all: the world’s first known split-seconds chronograph wristwatch, sold in 1923. The buyer, who paid just shy of $3 million for it, was in all likelihood Patek Philippe itself; when the brand takes over London’s Saatchi Gallery this spring for its fortnight-long Grand Exhibition – a truly landmark event for any British watch lover – it will be a star of the show.

Patek Philippe
Patek Philippe

This is exciting news, since few single historic watches from any brand retain such a footprint in the modern era. Not only is it the father of all split-seconds wristwatches – including legendary Patek Philippe references like the 1436 models produced from 1938 to the 1970s, and the 5004 perpetual calendar chronograph with split-seconds – but when Patek Philippe embarked some years ago on its project to establish a full suite of in-house chronograph movements, it went back to the source. Its debut in-house chronograph, reference 5959 launched in 2005, was essentially a recreation of the 1923 watch, movement and all – hence its 33mm (tiny by today’s standards) case size. The 5959 is spectacularly rare (it remains in the catalogue), though the movement, now designated CHR 27-525, is used also in the cushion-shaped, steel-cased 5950, and as the base for the 5151 Grand Complication.

Patek Philippe
Patek Philippe

Each of those references is priced considerably to the north of £300,000, and only a tiny number of each exists – this is true pinnacle stuff. But demand for split seconds chronographs among Patek collectors is such that there’s a clear rationale for producing something slightly more straightforward (in a manner of speaking) and serviceable, based on the chronograph movement Patek Philippe launched in 2009, the groundbreaking CH 29-535. And now, in ref 5370, that is exactly what we have.

Patek Philippe 5370
Gary Smith

What is a split-seconds chronograph anyway?

For the uninitiated, a split-seconds chronograph is one with two chronograph seconds hands, which sit one on top of the other. When the chronograph is activated, both move off together, the bottom hand invisible beneath the upper; when a separate button is pressed, however, one of them stops while the other continues – press the button again and it instantly catches up, until you stop it once more. The chronograph reset button returns both hands to zero. Also known as a double chronograph or rattrapante – from the French verb rattraper, meaning to catch up – it was developed in the 1860s for sports timing purposes (essentially anything involving laps).

Patek Philippe 5370
Gary Smith

While its function is less high-minded than a perpetual calendar or minute repeater, as a piece complex horology it ranks alongside those complications. Onto the normal chronograph requirements it adds (in very basic terms) an extra column wheel, an isolator mechanism, a clamp system acting as a brake, and a need for the most intricate fine-tuning. Alignment of the two seconds hands as they move together or instantly reset is devilishly tricky. As one respected horologist told QP: “There are various split-second chronographs around, but many of them don’t centre together completely – when you look at them moving round together you should only see one hand. That’s incredibly difficult to achieve – it’s probably the most difficult complication to realise in perfection.”

According to research by Daryn Schnipper, chairman of Sotheby’s International Watch Division who oversaw the June sale, the 1923 watch probably cost 50 per cent more to make as a split seconds than as a normal chronograph. Today’s economy of scale is, in fact, even more outlandish: at the £180,000 mark, the new 5370 is more than three times the price of its straight chronograph older sibling, the 5170. And by the way, Patek Philippe has announced a new black-dial version of that little beauty too.

The movement

The new 5370 split-seconds uses the same chronograph movement as the 5170, CH 29-535: a true bells-and-whistles masterpiece, with traditional column wheel system and horizontal clutch, and packed with minute innovations. In short, there is a kind of tranquil smoothness to the way it operates – the easy action of the pushers, the precise movement of the hands – that is deeply satisfying, coupled with a case-back view that’s utterly handsome. Upgraded to split-seconds functionality, it’s completely electrifying.

Patek Philippe
Patek Philippe

The 5370 isn’t in fact the first time we’ve seen this view: in 2011 came the upgrade to the 5004 perpetual calendar/split seconds chronograph, the 5204, which finally did away with bought-in base calibers and applied the same revolutionary thinking to the split seconds mechanism as the 29-535 did to straight chronograph technology. In particular – for those of a highly technical persuasion – this means a redesign of the way in which the split-seconds lever locks with the heart cam that connects it with the chronograph wheel, which according to Patek Philippe, amounted to a “75 per cent improvement in the congruence of the split-seconds wheel to the chronograph wheel”. So there.

Patek Philippe 5370
Gary Smith

But really, who’s counting? Well, those measuring the roughly £120,000 price leap between the straight chronograph and the split-seconds version of course. But looking at it in operation, as we did here at Baselworld yesterday, is enough to recognize horological magnificence. The Patek Philippe 5307 Split-Seconds chronograph is, frankly, stupendous, and one of the key watches of Baselworld 2015. Furthermore, it is a masterful continuation of one of the great stories in watchmaking.