Modern replica of the Staffelwalze, or Stepped Reckoner, a digital calculating machine invented by Gottfried Wilhelm Leibniz around 1672 and built around 1700, on display in the Technische Sammlungen museum in Dresden, Germany. It was the first known calculator that could perform all four arithmetic operations; addition, subtraction, multiplication and division. 67 cm (26 inches) long. The cover plate of the rear section is off to show the wheels of the 16 digit accumulator. Only two original machines were made, of which he single surviving prototype is in the National Library of Lower Saxony (Niedersächsische Landesbibliothek) in Hannover.