Offered is an authentic mid-19th century French mechanical perpetual pocket calendar, known as a “Clef-Calendrier” (calendar key). These ingenious personal calculating instruments pre-date widespread pocket watch ownership and allowed a gentleman to instantly determine the correct day of the week for any date.

Constructed of solid brass with hand-engraved lettering and original geared calendar disk mechanism. The side pin advances the internal ratchet gear which aligns the month arc and date aperture. The device is calibrated to the base index year 1842, typical of early French perpetual calendar instruments.

Front dial shows months in French with solar Sunday indicator. Reverse dial displays date window and weekly alignment index. Interior gearing remains intact and original.

These were carried alongside a watch chain or waistcoat pocket and represent one of the earliest forms of portable analog computing.

A scarce example sought by horology collectors, scientific instrument collectors, and early calculating device enthusiasts.