There are slides devoted to this topic: Lecture 2, pp. 44-48.

Websites

For biographical information on the German mathematician Gottfried Leibniz, read the  “Gottfried Leibniz” page from the History of Computers website.

Visit “The Stepped Reckoner of Gottfried Leibniz” on the same website to read a detailed account of the inspiration behind, the development of, and the later significance of the Reckoner.

“The Leibniz Step Reckoner and Curta Calculators” page at the Computer History Museum shows the relationship between the Reckoner, and the stepped-drum apparatus around which it was developed, and the creation of the Curta Calculators 250 years later.

The “Leibniz Wheel” Wikipedia page provides a computer animation of the wheel, as well as a list of post-Reckoner machines that adopted this device.

Other Media

Watch a Lego version of “Leibniz’s Stepped Wheel“, or stepped-drum, which was the mechanical base for the Stepped Reckoner

Books

The Universal History of Computing, Georges Ifrah, p. 125-126