Oskar (aka Oscar) Leuner (born about 1841) is a mechanical engineer from Dresden, who in 1870 established a workshop in his hometown. The workshop worked in the area of construction and manufacturing of scientific and technical instruments, mainly for Dresden Polytechnic College (Hochschule). Later Leuner established the Mechanische Institut of Oskar Leuner an der technischen Hochschule zu Dresden.
In the middle of 1870s Leuner devised a small calculating instrument (so called Addirstift—Adding Pencil), which he patented in 1877 (Patent DE2555 from 08.12.1877). The Addirstift of Leuner is similar to the earlier instrument for adding and registering numbers of Corliss from 1868 and Adding Pencil of Marshal Smith (US patent 175775 from 1876). The Addirstift was produced in small series, its price was 12 DM.
Let's examine the device, using the patent drawings (see below).
Inside he circular sleeve (marked with h on the drawing) is mounted a steel axis (g), fixed to the ending thick pin (n) by means of a round plate (h1). The pin is projecting from the front end of the device, limited by the plate (h1), which is in contact with the conical base of the sleeve. The pin is inscribed (at equal intervals) with the digits 0 through 9.
On the other end of the sleeve is mounted a square box, which hosts three 10-teeth ratchet wheels mounted on steel axes together with buttons (a, b, and c) and digital wheels, which can be seen through the three windows (d, e, and f).
The adding device of Leuner
Pressing the pin pushes the axis g up according to the distance (and the digit, marked on the sleeve's end). The rear end of the axis is firmly connected (by means of the teeth axis m) to the ratchet wheel of units (c). The axis g is fixed to a spring, which is returning it to the initial position after releasing.
The device can be zeroed using the buttons a, b, and c.
The tens carry mechanism is implemented by means of the three ratchet wheels (a', b', and c'), mounted on the same axes, as main ratchet wheels, buttons (a, b, and c) and digital wheels. The wheel of units (c') has only 1 tooth and is transferring the carry to the 10-teeth wheel of tens (b'), which is coupled with a 1 tooth wheel, used to transfer the carry to the 10-teeth wheel of hundreds (a').
The digital capacity of the device is up to 999, but it can easily extended, by mounting additional wheels in the square box.