"The big breakthrough in mechanical calculators came with the invention of new mechanisms to replace Leibnitz's stepped drum. Two men, in different parts of the world, created a variable-toothed gear: Frank S. Baldwin of the U.S. and T. Odhner, a Swede working in Russia. Both Baldwin (1875) and Odhner (1874 ) machines were produced. In 1892, the firm of Grimme, Natalis and Company A.G. of Braunschweig acquired the patents of the original Odhner pinwheel machine, which it manufactured under the name of Brunsviga."

Source: Dr. Tim Bergin American University Computer History Museum - Mechanical Computing

X-Number World of Calculators