The Adder Calculator consists of two interlocking metal dials, one small and one large etched with numbers around rotating internal components. There is a small open window where the two dials meet. The smaller side includes text "PATD NOV 5TH 12TH 1889". Text on the larger dial reads "The Adder" and "C.H. WEBB". There are five small to large rust spots on the back around the center opening of the smaller dial.