If you have about US$6 million going spare, you can put in a bid for a contender for the title of world's most complicated watch. On May 14 at Sotheby's in Geneva, one of only four existing Patek Philippe Calibre 89 watch/clocks goes on auction for the first time since 2009. Made to celebrate the 150th anniversary of Patek Philippe, the Calibre 89 has 33 complications or functions, making it the most complex watch constructed in the 20th century.

In horological circles, just which is the world's most complicated watch depends on what you mean. If it's the most complicated of all time, then the Vacheron Constantin Reference 57260 is the winner with 57 complications. If it's the most complicated of the pre-digital age when mechanical movements were the only way to make watches, then the Henry Graves Jr Supercomplication of 1932 with 24 complications is the one.

The Patek Philippe Calibre 89 with 33 complications sits in between these two champions. The first was completed in 1989, making it the most complicated watch of the early digital age, of the 20th century, and the most complicated watch made by Patek Philippe.

The yellow gold, double-dialed, and double open-faced watch has a diameter of 88.2 mm and weighing in at 1.1 kg (2 lb), it's a bit ungainly for practical use, but it was made to solve a bigger problem than helping someone tell the time. The 1980s were a low point for Swiss watchmakers. The digital revolution hit it hard as the microchip and LCD displays made possible the mass production of watches with numerous features and the accuracy of the finest chronometer at a cost so low that they could be given away as party favors.

Traditional firms were in danger of going the way of quill pen makers and buggy whip manufacturers. But in the 1970s, Vice President and Managing Director Philippe Stern of Patek Philippe saw the writing on the wall. He decided to redirect the marketing of the company's timepieces away from its usual customers and concentrate more on aggressive marketing to wealthier clientele who aren't necessarily well read on the topic of timepieces, but are impressed by mechanical marvels.

Part of this strategy involved reproducing the Henry Graves Jr Supercomplication to commemorate the 150th anniversary of Philippe Patek in 1989, but this was soon amended to creating a new watch that was even more complex that would act as a showpiece of what Swiss craftsmanship can do.

In 1980, design work began on the Calibre 89 and continued for five years. Traditionally, master watchmakers don't use blueprints and prefer to rely on memory and a lifetime of experience, but for the new watch, new methods were introduced. Detailed photos were taken of the Henry Graves Jr and the still-young tool of computer-aided design was used to produce a higher level of precision components for the complex movement. This also allowed the designers to make major changes to the watch by introducing a tourbillon escapement and multi-functioning crown without having to start from scratch.

Constructing the first Calibre 89 took another four years, with the first completed in April 1989. After that, three more in pink gold, white gold, and platinum were made over the next nine years..

The handmade Calibre 89 consists of 1,728 components and has nine more complications than the Henry Graves Jr. Supercomplication. Because the watch is so complex, it hasn't one movement, but four separated into four tiers on three plates that work in concert with one another. These are powered by three mainspring barrels for the watch and calendar, alarm, and repeat function. There's also a tourbillon escapement revolving at 0.5 rpm to regulate the mechanism.

The remarkable complexity can be seen by the mass of subdials and displays on the two main dials that cover the front and reverse of the Calibre 89. The Mean Time Dial is in cream with applied yellow gold Breguet numerals showing an outer track for minutes with red five minute divisions. There are subsidiary dials to record 30-minute and 12-hour intervals, the hour and minute hands are made of yellow gold and the second hand is blued steel.

Also on the Mean Time Dial there is the Winding Crown position indicator that shows what specific functions the watch is set for; a perpetual calendar that shows the day, month, year, and century and is accurate up to the 27th century with properly calculated leap years and the leap year cycle also indicated; split seconds; power reserve indicator; an adjustable second time zone; moon phases; alarm settings; and even the temperature.

On the other side of the watch, there is the white Sidereal Dial with Arabic numerals calibrated for 24 hours records sidereal time. There's also a transparent disc with gold dust used to represent the Milky Way on a celestial chart of the night sky over Geneva, Switzerland. A gold Sun hand rotates around the dial once a year to show the current sign of the zodiac, the seasons, the solstices, and the equinoxes.

In addition, the Sidereal Dial has readouts for the time of sunrise, the Equation of Time, and the date of Easter. Unfortunately, the cam controlling the latter needs replacing every 29 years, but there is an indicator to remind the owner of this once-in-a-generation chore.

All of this is sealed in a bassine case made of three pieces fabricated from 18K gold. It's interrupted by the winding crown and slides to control the alarm, repeater, and the petite sonnerie and grande sonnerie. The dials are protected by a pair of corundum sapphire crystals.

The Calbre 89 (Reference 989, Movement number 844000, Case no 2839425) comes with a fitted wood box with a plaque engraved "Calibre 89", as well as documents confirming the date of manufacture, a gold corrector, and gold key. It's being sold as the property of on unnamed private collector at the Important Watches sale at Sotheby's in Geneva on May 14 at 10:30 am CEST. The estimated price is 6,500,000 to 10,000,000 CHF (US$6,601,010 to US$10,155,400)

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