Notes: "Produx was a slide adder company in German that was founded by Otto Meuter, after he had previously worked designing slide adders for Addiator, the 800 lb. gorilla of the German slide adder market. After leaving Addiator in the early 1920s, Meuter founded a company with J. Bergmann to produce, what else?, slide adders. His adders were sold under the names ProCalculo! and Correntator. In 1928 he began to sell the Produx, which had a very long run. It continued to be made after World War II, and in fact this one is marked on the back in very faint blind stamped letters, “Made in Germany – West”. "