This instrument, made by Christian Boyling, consists of two superposed brass plates. The top plate is finely perforated and adorned with the coat of arms of the House of Saxony. We can glimpse a red silk backing. At the center of the plate is a circle divided into twenty-four hours containing three horary disks: a nocturnal based on the phases of the Moon, a perpetual calendar, and a zodiacal calendar showing the length of day and night throughout the year. Between the two plates is a rotating disk carrying twelve smaller enameled disks depicting the months (one missing). These appear one at a time through the small circular window below the three horary disks.