Stephenson's Pocket Adder

The two-wheeled versions were sold at least up to the end of 1920s under a number of different names (Perfection Adding Machine, Universal Adding Machine, Mindling Vest Pocket Adding Machine, etc.), made by different manufacturers (including the Stephenson's own workshop in Joliet, Illinois), which are sold in the end of 19th and the beginning of 20th century for $1-$2.

In the two-wheeled production version (see the lower photo), the user may enter only single digits in the right wheel. There is also an automatic carry to the left wheel, which registers up to 19, so that the maximum sum is 199. The Stephenson's adder seems to have been an aid for people adding long columns of figures using paper and pencil.

The two-wheeled version of Stephenson's Adding Machine

The device is only 3.5 inches long, 2-3 mm thickness, and is constructed entirely of brass. Numbers are entered by means of a pen. Reverse turn (i.e. subtraction) is not possible. Reset is done by manual forward rotation to 0.