The elements of the new mechanical CH 28-520 HU movement are the self-winding CH 28-520 PS chronograph caliber with column-wheel control and a vertical clutch as well as the proven World Time module based on a concept developed by Genevan watchmaker Louis Cottier in the 1930s. Subsequently, Patek Philippe further optimized this ingenious solution and had two important refinements patented in 1959 and 1999.
The chronograph movement and the World Time mechanism were enhanced with extensive modifications. Axes were shifted, bridges thinned and newly designed, and component clearances changed such that the caliber CH 28-520 HU can legitimately be called a new movement. It embodies everything that belongs to Patek Philippe’s watchmaking heritage while featuring technical and functional innovations that make it a latest-generation movement.
This also applies to its operation, in line with Patek Philippe’s commitment to user-friendliness. The chronograph has a start/stop pusher at 2 o’clock and a reset pusher at 4 o’clock that also doubles as a flyback pusher. When it is pressed while the chronograph is running, the sweep hand flies back to zero and a new time measurement is started automatically. Because the chronograph hand is powered via a vertical clutch, it can also be used as a permanently running seconds hand without risking undue wear and without affecting the rate accuracy and power reserve of the watch.
A look at the dial shows how seamlessly the two complications are integrated. The outermost display element in blue lists the 24 city names that each represent an entire time zone. It has been updated with new cities for some time zones – for instance Dubai instead of Riyadh or Brisbane instead of Nouméa – and takes into account the fact that Moscow changed its local time from UTC+4 to UTC+3. A small gap between the city disk and the 24-hour ring accommodates the seconds scale for chronograph measurements. It is a narrow white circular scale with fourth-of-a-second graduations. This subdivision reflects the movement frequency of 4 hertz (28,800 A/h), which allows times to be stopped to an accuracy of one-eighth of a second.
The World Time function is also very easy to use: The hour and minute hands indicate the time in the city and time zone whose name is shown at 12 o’clock. The time in the 23 other zones can be quickly and easily determined with the city disk and the two-coloured 24-hour ring which instantly tells the user whether it is day or night in the respective city and time zone. When traveling from one time zone to the next, pressing the corrector button at 10 o’clock advances the city disk and the 24-hour ring counterclockwise in one-hour steps as well as the hour hand clockwise, also in one-hour steps. The correction is finished when the city name of the destination time zone is at 12 o’clock. During this process, the World Time mechanism and the hour hand are uncoupled from the movement, so neither the amplitude of the balance nor the steady progression of the minute hand are affected. The chronograph hand also keeps moving without the slightest irregularity.
Caliber CH 28-520 HU
Self-winding mechanical movement, column-wheel chronograph, vertical clutch, local time, display of 24 time zones, day/night indication, 28,800 semi-oscillations per hour (4 Hz), Spiromax balance spring
The new Patek Philippe World Time Chronograph Ref. 5930 launches in 2016 in a version with a 39,5 mm white-gold case and a blue, hand-guilloched dial center.