How it works:

The moon phase and date

The moon phase and analog date mechanisms are of a unique construction that uses very little energy. Both the moon phase and date are advanced in periodic jumps by twin trains of wheels and pinions, geared according to the lunar cycle and 24 hour cycle respectively. The date change is completed in one hour.

The moon phase mechanism is as simple as it is precise. It takes 122 years and 45 days to accumulate the error of a single day.

A safety device prevents the movement being damaged by manual intervention during the automatic date change.

The wheel trains for the moon phase on the right, and for the date (left) are both driven from the intermediate wheel (A).

The moon and the date are moved forward one jump every 24 hours by finger pieces B and B1. In each case, the freely turning finger pieces are driven round by the pins (C and C1) mounted on the carrier wheels for the moon (D) and for the dates (D1).

The finger pieces engage the 7 pointed star wheel for the moon (E) and the 31 point star for the dates (E1), pushing them one notch forward against the jumper springs F and F1.

The pinion mounted on the moon star wheel (E) is geared with the toothed rim of the moon disc G, moving the moon on the dial to a new phase.

The dates hand pointing on the dial is mounted directly on the dates-star E1 through the moon disc.

Both the moon phase and the date can be advanced manually by push pieces in the case band acting on the sprung levers H and H1. The end of each lever engages its respective star wheel to move the moon or the date one 24 hour step forward against the jumper springs.

Safety device

If the date is advanced manually when the finger piece B1 is about to engage the dates star E1, there is a risk that a point of the star will butt against the point of the finger and jam the movement.

To avoid this, a spring (K) acts against the special profile of the finger piece B1, positioning it so that it never encounters the dates-star E1 at an unfavourable angle.

Power reserve indicator

When the mainspring winds up, the power reserve wheel (L) turns clockwise as far as its arc of teeth will allow. This takes the power reserve hand up to 48 hours on its scale.

As the barrel unwinds, the planetary gears reverse the rotation to turn wheel L to the other end of its arc of teeth.