Moon-phase display A disc that rotates under the dial and is visible through an aperture. It shows the moon phases from full to new, generally as seen from the Northern Hemisphere.

Lange's perpetual calendar with the outsize date and day-of-week, month, 4-year/leap-year and | moon-phase displays has a truly convenient feature: The displays can be advanced either separately or collectively with a practical main push-piece. The | moon-phase display has been computed to such a degree of accuracy that the aggregate error is only one day in 122.6 years of uninterrupted operation.