He developed a compact symbolic notation to describe the topology of a very wide variety of mechanisms, and showed how it could be used to classify them and even lead to the invention of new useful mechanisms. At the expense of the German government, he directed the design and manufacture of over 300 beautiful models of simple mechanisms, such as the four-bar linkage and the crank. These were sold to universities for pedagogical purposes. Today, the most complete set are at Cornell University College of Engineering.