Patek Philippe invented the combination complication of chronograph and perpetual calendar with the ref. 1518 in 1941, starting a lineage of very desirable timepieces. But the chronograph perpetual calendar with the greatest lifespan was the ref. 3970, produced from 1986 to 2004.

Because it was in production so long, nearly 20 years, the ref. 3970 is the most common of the chronograph perpetual calendars made by Patek Philippe. The upside of that is that the ref. 3970 is the most affordable, relatively speaking.

By far the most common is the third series, but the most beautiful are the first and second series 3970s. The most obvious difference being in the feuille, or leaf, hands of the first and second generation. This small but significant detail gives them a look that closely approximates that of the immensely valuable ref. 2499, the immediate predecessor of the ref. 3970.

Pictured here is a second series ref. 3970 in rose gold. Unusually this is a ref. 3970 with a screwed-down sapphire display back, an uncommon feature. Most of this series with sapphire backs are ref. 3971, identical save for the model reference.

Throughout the production of the 3970 it retained the same 36 mm case, though the case back went from snap-on to screw-down. Another key difference was the presence of prominent hallmarks stamped on the flanks of the lugs (instead of on the underside as is common), a feature found on the gold second series and one prized by collectors.

Like the rest of the 3970, this second series watch has the calibre CH27-70 inside , built on a Lemania 2310 ebauche, or movement blank. Though it is a finely finished and beautiful movement, the movements are the least studied aspect of the reference as they remained almost unchanged throughout the production of the ref. 3970.

Intriguingly, the second series ref. 3970 does not sell for all that much more than the far more common third series. Collectors have long speculated that the price differential should rise, given the rarity and aesthetics of the second series, but that has not happened. The third series sells for between US$75,000-90,000, while the second series can be as little as 10% more, making it a very attractive proposition.

A watch with two faces, the Montblanc Metamorphosis II transforms from one dial to another in five seconds, going from showing the chronograph to a date display, driven by an extraordinarily complex mechanism with nearly 500 parts.

Unveiled a few years ago as the TimeWriter Metamorphosis, Montblanc has revamped the timepiece to create the Metamorphosis II. It has been given a more restrained, classical aesthetic with a silvered guilloche dial.  The movement, however, remains the same, utilising a mechanism similar to that of a minute repeater to power the transforming dial. It is an enormously complex module built on the MB 67.40 chronograph movement. Most of the movement’s constituent parts, 494 of 746, are for the transforming mechanism. Originally designed by a pair of watchmakers but delayed several years due to difficulties in production, the Metamorphosis movement is complex but functions on a simple principle. Pushing a slide in the case winds up a small spring which then drives the dial transformation, with wings that open and close to reveal different functions.

The under-dial mechanism of the Metamorphosis

When the wings are closed, the sub-dial at six shows the date, and once activated the wings retract under the dial to show a chronograph, with the chronograph sub-dial rising up at six o’clock. Once that happens the central seconds goes from being a constant seconds to the elapsed seconds hand of the chronograph. The transformation takes just five seconds. 

Regardless of the state of the dial, the date and chronograph functions continue to run as they should. So if the date is shown on the dial, but the chronograph is left running, once the chronograph is revealed it will show the correct elapsed time.

The time is displayed regulator-style, with the hours in a sub-dial at 12 o’clock, with minutes on a retrograde scale on the main dial. The minute hand travels from eight o’clock to four o’clock before jumping back to zero. This video illustrates the function of the TimeWriter Metamorphosis, which works exactly the same as the Metamorphosis II. Beyond the dial, another major change is the case design. The Metamorphosis II has a 52 mm round case, unlike the odd shape of the first model, which had an oval form with a bulge at six o’clock. The Metamorphosis II is priced at 404,800 Singapore dollars, equivalent to US$317,000.

Arguably A. Lange & Söhne‘s most recognisable timepiece, the Lange 1 is the face of the brand. For the 20th anniversary of the model, Lange has created five different sets of the Lange 1, comprising matching his-and-hers Lange 1s with guilloche dials in colours used on earlier Lange 1 models but not seen since, like a black dial with a rose gold case.

Each set is made up of the classic 38.5 mm Lange 1 and the Little Lange 1 which has a 36.1 mm case and a diamond-set bezel. Unlike the conventional Lange 1 which has a smooth, satin finish dial, the anniversary editions have guilloche dials, bringing to mind uncommon, earlier Lange 1 limited editions like the Lange 1A.

While this use the standard Lange 1 movement, a small detail sets them apart – the balance cock has an engraved “20” in a nod to the anniversary.

These will be available in platinum with a silver or black dial, or white gold with a blue dial, or pink gold with a black or silver dial. Only 20 sets of each metal will be made.

The prices are as follows: US$98,100 for the pink gold, while white gold is US$100,500, and platinum will cost US$122,900.

“Shape Your Time” is a short video inspired by Cartier’s watchmaking, with clever animations, dramatic music and many references to the brand’s history.