Zenith El Primero Chronomaster Power Reserve Gold (18.2080.4021/01.C494)

Ian Fleming, From Russia, with Love

The watch in question belonged to Nash, one of the most dangerous SMERSH killers. James Bond manages to take it from him at the end of the story. So, gadget or not, what about the moon-phase indicator? Or in other words, does it help to know the moon's phases? This is a huge debate and one that has preoccupied all kinds of more or less informed scientists for centuries. Here for example are two proven scientific phenomena that open the door to all sorts of interpretations: 

- Moon rays penetrate the earth more deeply than their solar counterparts.

- The earth's magnetic field diminishes before the full moon and increases afterwards.

In the first case, it is in agriculture (and in bio-dynamics in particular) that the phenomenon has been most closely examined by establishing calendars that indicate the best periods for sowing, planting and harvesting according to the different moon phases. 

In the second, it appears that certain migratory animal species use magnetic variations to establish a virtual geographical map and thus find their way when they are on the move. 

Going back to watchmaking. Contrary to the month, the hour or the minute, which are human inventions, the day and lunar period are natural time cycles. It is therefore logical that they were the first to be reproduced by man with the clocks and pendulums that appeared in the Middle Ages. Remember that at this time, common mortals did not know how to read, write or count: these cycles therefore had to be indicated analogically. For the day, it is easy for somebody illiterate to understand that the progression of a single hand going in the direction of the top of the dial (zenith) in the morning, and its descent to the bottom in the afternoon, corresponds to the path of the sun.

As regards the longer and therefore less understandable cycle of the moon, people sought to reproduce as faithfully as possible - also by analogy - what they could see happening in the sky. The most commonly used manner up to now is to make the moon move from left to right in a window of a particular shape. Usually, a wheel with 59 teeth (2 x 29.5 days) is hidden behind this, thus completing a rotation in 59 days, featuring two moons appearing one after the other in the window. 

However, it is important to recall that the exact length of a lunar period is not 29.5 but 29.53 days. There is therefore an error of 0.03 days per cycle, which has to be corrected by a day every two and a half years. Other mechanisms that are more sophisticated and reserved for high-end watches require only one correction every century, or less. It should be noted that, very selfishly, this system only works for half the Earth: the Northern hemisphere. Indeed, in our part of the world, the moon is said to be a liar: it forms a D when it rises and a C when it decreases, and that is what is seen in the window. On the other hand, for an observer in the Southern hemisphere, thus upside down, it is exactly the contrary! Curiously, a Girard-Perregaux watch with a double moon phase designed in the 1980s and which corrected this "injustice" was only a mild success. 

Finally, if there were any doubt as to the influence of moon phases on our human behaviour, the numerous moon-related expressions in various languages would certainly not exist. Moreover, there are countless examples of phenomena that we attribute to the most important moment in the cycle: the full moon… beware of werewolves! So the watch that 007 helped himself to was in fact much more than a gadget!

Willy Schweizer is Curator of the Girard-Perregaux Heritage.