On 23 April 1873, Ferdinand (also spelled as Friedrich or Franz) Hebentanz, from Budapest, obtained a privileg (patent) in Austria-Hungary for several adding machines. In fact, in the patent are described three different devices: keyboard adding machine without engine, keyboard adding machine with engine (spring motor), and pointer (pen-setting) adding machine or totaliser. In October of the same year, one of adding machines of Hebentanz was presented and received an award at Weltausstellung 1873 Wien (World Exposition 1873 in Vienna).
The second machine, also known as Bieringer und Hebentanz Tastertur Aditions Maschiene is a single-digit keyboard adding machine (i.e. having the capacity for adding but one digital column at a time) with a clock mechanism (spiral spring) drive. It seems several devices had been manufactured and one of them managed to survive our time (see the lower images). There is also an example of Hebentanz keyboard adder at the collection of Arithmeum Museum, Bonn, which created a very good animation for the device.
When a key of the device is pressed down, the spring power is released and can have an effect on the wheels of the result mechanism—longer or shorter, depending on the digit that has been entered. The mechanism is well-designed and operating the keyboard is very comfortable and smooth. Winding up the spiral spring once, using the mounted lever with a circular handle on the left (see the nearby image, as in the lower images this lever is mounted on the lid of the wooden box), makes calculating possible for an astonishingly long period of time, so that this additional step does hardly count, compared to the use of other single column key adding machines.
We don’t know who was the inventor of this machine. He would be Ferdinand (Nandor) Hebentanz (born 1848, died 19 August 1914), who at the end of the 19th century worked as Rechnungsführer (chief accountant) of Budapest Sparkassa (Savings Bank). Nandor Hebentanz definitely needed such a machine for his daily work as a young accountant in the early 1870s.