Circular Slide Ruler

Instrument signed "CH. CHARPENTIER, Breveté SGDG", France, circa 1890-1900. Steel and bronze engraved in long-grain leather case.
Circular pocket ruler engraved with 5 scales in Roman numerals and Greek letters, in its original case. Manual rotation mechanism. In its original case with the manufacturer's name engraved in gold letters. The back of the instrument also bears the words "Circular slide rule" as well as the name and mention of the patent. We have not found a model similar to this rule, however a "Calculimeter" signed G. Charpentier comes close to this model. Some points of wear. The detached upper circle probably housed protective glass.