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The Millennium Watch Book
Omega  - Seamster Ploprof 1200M Co-Axial Master Chronometer

Omega Seamster Ploprof 1200M Co-Axial Master Chronometer

Discover this exclusive extract from the Millenium Watch Book. A Legendary design especially for professional divers

Although the Omega Seamaster first saw the light of day in 1948, it really became a genuine dive watch in 1957 when the brand created three professional ranges: Seamaster, Railmaster and Speedmaster. At that point it took on all the attributes of the modern diving watch, including enhanced water resistance, a rotating bezel and easy readability. However, the growing practice of saturation diving in the 1960s created the need to develop even more effective high-tech instruments. The high pressures experienced at great depths make the air toxic, so divers must breathe a mixture of helium and oxygen to reduce the danger of narcosis. As one of the smallest elements, helium runs the risk of entering a watch even when water or oxygen cannot. During time spent at great depths or in a pressurised environment, the pressure inside the watch gradually equalises with the pressure in the diving suit or diving bell. As a diver ascends, the return to surface pressure may cause the watch’s crystal to burst off.

A Unique Set of Characteristics

In the 1960s, Omega started to work with Compagnie Maritime d’Expertise (better known as COMEX), launching a programme known as Ploprof (a contraction of plongeurs professionnels, professional divers). The name encapsulates the mission statement: creating models in collaboration with professional divers, for professional divers. Among the various solutions examined, the Ploprof 1 gave birth to an iconic watch: the Seamaster 600 Plongeur Professionnel, first marketed in 1971. It stands out due to its imposing dimensions (55mm wide and 13.5mm thick) and a unique design structured around an asymmetrical case made from ‘Uranus’ 904L stainless steel. To prevent helium entering the watch, a single-piece construction was adopted. The Ploprof was presented as being water-resistant to 600m, but has been tested at pressures exceeding 1,300m. Another distinguishing feature is its original bezel locking system. While the bezel is bidirectional, it can be rotated only by pressing on the coloured pusher at two o’clock. The crown is located at 9 o’clock and protected by an imposing crown cover. Its unique position ensures wrist movement is not impeded and prevents any inadvertent adjustment.

This iconic dive watch and its unashamedly vintage design made a comeback in 2009 with the Seamaster Ploprof 1200M, followed by a new edition in 2016 featuring the same distinguishing marks, ethos and outsize dimensions as the original model, whilst delivering extreme performance and incorporating a number of technical advances. 

Seamster Ploprof 1200M Co-Axial Master Chronometer

Seamaster Ploprof 1200M Co-Axial Master Chronometer © Omega

As its name suggests, the case of the Ploprof 1200M Co-Axial Master Chronometer is water-resistant to 120 bars (1,200m), and made from grade 2 titanium to ensure it is lightweight, robust and corrosion-resistant. The bidirectional rotating bezel, still activated by a safety pusher at 2 o’clock, is now fitted with a ceramic chapter ring on which the numerals, triangle and scale have been coated with Super-LumiNova®, making them easier to read in the dark. The scratch-resistant sapphire crystal has anti-glare coating on both sides. 

Another major change concerns the case: single-piece construction has been dropped, and instead, a helium valve at 4 o’clock allows any build-up of this gas to be released on decompression. In addition, the caseback is now transparent, revealing the Omega Co-Axial 8912 automatic calibre boasting the brand’s exclusive arabesque Côtes de Genève finish. The movement is Master Chronometer Certified by Swiss Federal Institute of Metrology (METAS), and meets stringent specifications, including resistance to magnetic fields of up to 15,000 Gauss. Its balance features a silicon hairspring and oscillates at 25,200 vibrations per hour; two series-mounted barrels provide a 60-hour power reserve. The automatic winding mechanism is bidirectional. 

The Seamaster Ploprof 1200M comes with a ‘Sharkproof’ brushed titanium Milanese mesh bracelet, combining comfort and strength. A dual-extension system with 18 positions allowing adjustment of up to 26mm enables it to be worn over a diving suit. The watch comes in a presentation box and is accompanied by an additional black rubber strap. 

This year GMT Magazine and WorldTempus have embarked on the ambitious project of summarising the divers watch since 2000 in The Millennium Watch Book - Divers watch, a big, beautifully laid out coffee table book. This article is an extract. The Millennium Watch Book - Divers watch is available in both French and English here:


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A company of the Swatch Group, OMEGA has been behind major revolutions in watchmaking technology and the timekeeping of numerous Olympic Games. Its watches are worn by world-famous celebrities and have travelled to the moon, the depths of the ocean and everywhere in between.

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