Precise phase of the moon indications deviate from the synodic or mean moon by one day after a couple of hundred years; Andreas Strehler's phase of the moon after two million years. This has won the Sauterelle à lune perpetuelle an entry in the Guinness Book of World Records.
However, all phase of the moon indications have a common problem: As precise as they may be, they cannot be read very precisely: Except at new moon and at full moon, the wearer of the watch has to guess what the exact phase or age of the moon is. Also the exact setting of the moon phase indication is only possible at new moon and full moon.
Moon Vernier Scale
On the dial of the watch, there is a conventional phase of the moon indication and the additional age of the moon indication with its moon vernier scale at six o'clock. On this high precision moon age scale, a red arrow indicates the age of the moon in days. Two red marks on the scale indicate new moon and full moon. A vernier scale on the inner vernier ring increases the accuracy of the indication to three hours.
- The red arrow indicated the age of the moon in days.
- If the arrow points to a number in the blue sector of the outer scale, the accurate value is alsoread from the blue sector of the inner vernier ring. The age of the moon accurate to three hours is indicated where the next mark on the vernier ring aligns with a mark on the outer ring.
- These hours are added to the days indicated on the outer ring.
In the same way, if the red arrow indicates a day on the yellow sector of the outer scale, the hours are also read from the yellow sector on the vernier scale. A patent is pending for this moon vernier scale.
Patented remontoir d'égalité
In addition to the patent pending moon age indication, the Lune exacte also has Andreas Strehler's patented remontoir d'égalité, first presented in the Sauterelle.
Conventionally, a complication known as force constante (constant force) acts on the escape-wheel. However, this is the point in the whole movement where the least torque is present.
For this reason, Andreas Strehler's remontoir d'égalité is attached to the seconds wheel or fourth wheel. Every second the visible satellite gear provides exactly the same amount of energy to the seconds wheel and at the same time displays the seconds as dead-beat seconds. The energy is accumulated by a star-shaped satellite through a spring which is re-loaded every second. Then, the satellite wheel is released and transfers its energy to the balance. The satellite wheel then rests again against the palette-stone. This planetary design of the respective wheels is a first in a wristwatch.
This solution has the advantage that the complete escapement including the escapement wheel oscillates free from any influence between the individual impulses delivered by the remontoir d'égalité. Hence, the Swiss Anker Escapement performs without influence from the remontoir d'égalité, with its precision perfected over the last 200 years.
Fluctuations in the energy supply as well as flaws in the functioning of the gear train (uneven working of the mainspring, the gear train or the motion-work of the hands) are filtered and equalised by the remontoir d'égalité. In contrast to a force constante and its fixed division ratio, which demands a frequency of 18.000 A/h, the Remontoir d'égalité can be used with any frequency. The Sauterelle therefore has a frequency of 21.600 A/h which leads to higher precision.
All watches made by Andreas Strehler show an almost linear force path as the running down of the two mainsprings is limited by a epicyclic gear. Only the optimal part of each mainspring is used where the thrust produced is constant. With the Remontoir d'égalité, Andreas Strehler concentrates on the elimination of external factors such as temperature. Even minor changes in temperature influences the viscosity of the lubricants used in the mainspring barrels and consequently the even running down of the mainsprings.
With the Remontoir d'égalité, Andreas Strehler presents a mechanical solution which filters almost all technical and mechanical influences on the escapement.