Friedrich Oskar Leuner (1845-1930), known as Oskar (or Oscar) Leuner, was 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 (since 1876) for Dresden Polytechnic College (Technischen Hochschule). Later Leuner’s workshop evolved into the Mechanische Institut of Oskar Leuner an der technischen Hochschule zu Dresden (see the nearby ad from 1907), which existed until the death of its founder.
In the middle of 1870s Leuner devised a small calculating instrument (so-called Addirstift—Adding Pencil), which he patented in 1877 (German patent DE2555 from 08.12.1877). The Addirstift of Leuner is similar to the earlier instrument for adding and registering numbers of Charles Corliss from 1868 and Adding Pencil of Marshal Smith (US patent Nr. 175775 and Nr. 180949 from 1876). The Addirstift of Leuner was produced in small series in his workshop, its price was 12 DM (as a comparison, the Adding Pencil of Smith was manufactured in St. Louis, and reportedly some 5000 units were sold, for 5 USD).
Let’s examine the adding instrument of Leuner, using the patent drawings (see below). Inside the 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).
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 returns it to the initial position after releasing.
The device can be zeroed using buttons a, b, and c.
The tens carry mechanism is implemented using the three ratchet wheels (a’, b’, and c’), mounted on the same axes, as the 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 be easily extended, by mounting additional wheels in the square box.