Mission Impossible Hunted:

The Official Watch of the Musée International d'Horlogerie, La Chaux-de-Fonds

by Magnus Bosse
September 2005

Part 2
Click on small image to view large ones!

3. The Annual Calender:

This very straight-forward calendar mechanism is truely reduced to the max: Only 9 moving parts account for a sophisticated, yet highly practical complication. The calender displays the correct date (date, month, weekday) throughout the year, that means the mechanism correctly distinguishes between months with 31 and months with 30 days - it cannot calculate correctly the 28/29 days of February (this is what a perpetual calender masters).
The ingenuity of this mechanism is that it displays the complete date on 3 concentric discs: starting at the center of the watch, the weekday, the month and finally the date is displayed. This layout allows that two gear trains can act on the calender: the date train of the base movement Valjoux 7750, which switches the date and - at the 31st - the month discs at midnight, and the hour wheel, which turns twice every day (logically!), and switches the weekday disc twice a day shortly after midnight, and under certain constellation (months with only 30 days), also the date. The fact that the mechanical design switches the weekday disc twice a time is consequently used to add an AM/PM indicator, helping to correctly set the time of the watch, by using two dots left to the date window: One red dot - AM (top image), two red dots - PM (bottom image):

How does the calender now do its magic? The central element of the calender mechanism is a 3-layer column wheel (yes! A Valjoux 7750 with a column wheel, but not where most people expect it to be!). Layer 1 couples the weekday disk with the month disk, layer 2 is driven by a stud plate on the hours wheel, and layer 3 advances the date under certain conditions - in months with only 30 days. At the end of these months, the date is advanced by the conventional date mechanisms of the base movement and by the hours wheel via weekday and months switch.

Sounds complicated? Now let's go through the design step-by step and see how it works. We'll start with the basic Valjoux date switch and slowly add one layer after the other.

The basic Valjoux calender mechanism advances the date disk once a day, precisely at midnight. You can see the (unique) date disk (4) and the stud plate attached to the hours wheel (1). Also, the spring assuring the perfect centering of the date disc in the date window is visible. This spring is the only part left from the Valjoux movement's date mechanism that is visible here. Please note that the date disc has two teeth at the 10 o'clock position - they interact with the month disc only on the 31st and thus switch the month!

Now let's add the 3-layer column wheel (2) and a connector wheel (3). As you can see, the column wheel is driven by the hour wheel and is thus advanced twice a day to advance the weekday disc. The connector wheel ensures that the months disc is moved one month forward at the 31st. The gray space in the middle is left for the months and the weekday discs.

Now, the months disc is fixed (5). The connector wheel (3) now interacts with the gearing of the months disc (see arrow).

I hope I was clear so far. Let's recapitulate what I mentioned so far: The date disc is advanced once a day around midnight by the Valjoux's own date mechanism. On the 31st, the date disk advances thew month disc for one position via the connector wheel. On the hour wheel, a stud plate moves the 3-layer column wheel twice a day (8-column layer), which in turn directly advances the weekday disc:

But how is the date switched in months with only 30 days? Well, we haven't used the the thrid layer of the column wheel and a certain feature of the months disc I haven't told you yet: 5 horns, solely on months with only 30 days... please note the brass coloured ring below the months printing:

You easily will find the 5 horns (of which 4 are visible, see arrows), and they interact with the remaining layer (3) of the column wheel: In the particular position above (which is a position of a 30 days month), you can see the layer (3) of the column wheel interacting with one horn of the months disc. This disc advances on the 30th of the month in question (here September), and the month wheel then also moves - using the connectopr wheel described above - the date one day further. Since the date is also advanced by the movement's date mechanism, it moves two days at once: From the 30th shortly to the 31st and immediately to the 1st. That's it! A highly puristic mechanism, brilliantly thought-off, and very versatile. I should mention here that the two advancements are not performed simultanously: the date switch, as already mentioned, moves around midnight, but the weekday disc only a little bit later. So for a very short time there is the wrong date displayed. I guess still an amazing achievement, and only 9 moving parts are involed! An instant switch mechanism would require much more parts, and therefore would take apart much of the elegant beauty of this construction!
Another remark: as you could see, the mechanism is entirely operated by wheels. This means that you can advance and reverse the date and time without damaging the movement. Try this with a 'standard' annual or perpetual calender!

4. The Chronograph Monopusher:

This is actually quickly done - so it seems: 'Simply' a modification from bi- to monopusher, and a window at the back... wrong! True, it is not the most complicated modification, but a quite distinct one. The most delicate modification is applied on the chronograph cam. To ensure that this cam manages to control the chronograph as a monopusher (fixed sequence start-stop-reset with one pusher), the cam has to be modified in order to carry a new mechanical programme - that for reset as well. To this end, Paul Gerber added a few kerfs in the cam (see arrows in large picture below; left:, standard cam, right: modified cam). The modified cam then replaces the existing one (small images, left).
To view the minute counter information, a more subtle solution than a sub-dial had to be developed in order to keep the minimalistic design of the watch face. Paul Gerber opted for a window at the back, allowing you to view the minute counter wheel, which has a 30min scale added on it. A red arrow indicates the counted time (small images, middle and right).


5. The Manufacturing:

All parts, really all!, are made in Switzerland! The list comprises of nearly all renowned names of the Swiss watchmaking industry. All of them thankfully agreed to spare resources for this ambitious project. As this is not self-evident, I want to list all the suppliers here:

- base movement Valjoux 7750: Swatch Group, Biel (ETA)
- titanium case: Queloz SA, Saignelégier
- crown: Pibor ISO SA, Glovelier
- dial: CADOR, Eimeldingen, and MOM Le Prélet SA, Les Geneveys-sur-Coffrane
- hands: Universo SA, La Chaux-de-Fonds
- rubber strap: Biwi SA, Glovelier
- buckle: Cornu SA. La Chaux-de-Fonds

All the parts of the calender and the chronograph (modified parts) are entirely produced by Paul Gerber and his watchmakers in his Atelier in Zurich. So no anonymous workshop is doing the final job, but a true and world-wide respected master watchmaker, member of the AHCI, is laying his hands on each and every MIH watch. A truely unique situation! Below you can see all the parts that are made in Paul's atelier:

In particular, I want to draw your attention to the calender discs (small images, left; bare brass (bottom) and printed (top)) and the 3-layer column wheel and the connector wheel (small images, middle). You can also see two fixing plates holding the calender module (small images, right).


Finally, detailed images of the hour wheel which carries the stud plate driving the weekday disc. First, a distance ring is fitted to the hour wheel with two screws (top image), and then the stud plate with the stud plate finger is attached using the remaining two screw holes (below).

For this project, Paul had to slow down the production of his own RetroTwin and Cal. 33 watches. But he did it with joy and pride, as did his watchmakers. Here is Paul discussing with one of his watchmakers, Roland Hohl. Look at what's on Paul's wrist:

After this highly technical part, let's have some fun and join an important event at the Musée International d'Horlogerie, La Chaux-de-Fonds: The presentation of the MIH watch on September 9, 2005! Please follow me to part 3!

Part 1 - Introduction and design
Part 2 - The Annual Calender and the Chronograph Monopusher
Part 3 - The Presentation of the Watch at the MIH 09.09.2005

Part 4 - Three years MIH Watch! The Interview with Beat Weinmann