Slide Adder (1847)
|"Apokin, Igor' Alekseevich. Maistrov, Leonid
Efimovich, Razvitie vychislitel'nykh mashin (US Library
of Congress translitteration, freely translated:
Development of calculating machines and computers). 1974.
398 p.,  fold. leaf : ill. ; 22 cm.
The upper part is for addition and lower part for subtraction. The device has been designed for Russian currency, because of the units Ryb (ruble), K (kopek) and evidently a quarter of a kopek coin has also been available. According to the book Kummer was a music teacher in St. Petersburg, but any other information, for example his first name is not given."
Source: Timo Leipala