This seldom found treasure is a G. N. Mindling Adder in steel with Nickel Plating Adder Calculator in original packaging with direction sheet.   It is an unauthorized copy of the Stephenson adder, calculator that dates to late 1890s to early 1900s.  These little adders were popular for shoppers.   This is a very rare model that is stamped G.N. Mindling; Manufacturer; Pittsburgh, PA.   The more common Stephenson model is pictured and described in the book “Antique Office Machines” by Thomas Russo.  It is called a small cogged disk adder of the Pascal Principle.  The front has a decorative trim around the two disks with 10s carry over.  This rare and seldom found treasure is in very good condition with light pitting and operational (Calculates 1 to 99 with 10s carry over).  There is slight wear on Nickel plating, but still in beautiful operating and display condition.   Size is 3.5” x 2”.   This will highlight any old calculator collection.