Concept:A stepped reckoner is an early mechanical calculator invented in the 17th century.Explanation:Gottfried Wilhelm Leibniz built the stepped reckoner around 1672 to perform addition, subtraction, multiplication, division, and square roots.William Schickard made an earlier calculating machine, but it was not called the stepped reckoner.Herman Hollerith and John Von Neumann are known for later computing contributions.Answer:A. Gottfried Leibniz.