This is an exceptional watch with a moon phase display which deviates only by a single day after more than 1,000 years. It displays the moon viewed from the northern hemisphere in a large window on the dial. Depending on the relative positions of the moon and the sun, we see different positions of the illuminated half of the moon.
These positions are called phases of the moon. The phases indicated on this watch are marked in a unique way and can be set and calculated to the minute. One orbit of the moon around the earth, after which the moon resumes the same position in relation to the sun, lasts for 29.53059 days on average. To be more exact: 29 days, 12 hours, 44 minutes and 2.9 seconds. The complicated gear train of the Perpetual Moon translates this interval so precisely that the resulting deviation is only 0.23 seconds per day, or a whole day after 1,027.30 years.
In the Perpetual Moon, the phases of the moon are displayed inside the window on the dial at 6 o’clock. This consists of the moon phase disc with the eight internationally established astronomical phases of the moon marked as vertical lines, as well as a division into days applied to the dial. The moon phase disc shows the phases of the moon. A defined phase is indicated in such a way that the associated line on the moon disc lies precisely between the two triangles of the dial aperture. In order to achieve the extraordinary display accuracy, the moon disc must be securely attached to the hour indicator and run with it continuously. Nevertheless, the moon phase may be corrected via a discrete pin push-button at 9 o’clock without interfering with the time display. This causes one of the 8 moon phases to be advanced on each occasion. A wrap spring clutch – used here for the first time in a moon phase display – does precisely that. Precise setting of the time for the moon phase is performed via the crown. The Perpetual Moon phase is adjustable at any time via the pin push-button and the crown. Additional orientation between day and night is provided by a small central hand rotating once every 24 hours, with the first right half, the indices 12 to 6, indicating AM and the second left half, the indices from 7 to 11, indicating PM.
The watch, with a diameter of 40.8 mm, has the typically elegant appearance of a Moser watch with a dark blue fumé dial, and appliquéd details in the same colour as the case and the same treatment for the hands. A generously dimensioned power reserve display, subdivided into days, on the movement side completes this watch. A dual spring barrel guarantees a running time of at least seven days when fully wound. Of course, this watch also features the typical Moser escapement. The H. Moser HMC 348 movement is a hand-wound movement with an extra-long power reserve, with true bevel wheels for gentle, low-wear winding and Moser teeth in the entire wheel train. Screwed gold mounts and Moser ground stripes also visually accentuate the movement that is visible through the sapphire glass back.