7. แแฃแแชแ, แแฆแแแฉแแแ, แ แแ แแแแแแแ แแแฌแงแแแแแแแ แแฃแแแ แแแ แแแแแ แแแแแแแขแแแแกแก แแ แแฆแแแกแแแแแ แแแแแแแชแแแแ แแแแก แแ แแคแแกแแ แก แแแแฐแแ แจแแ แแ แแก, แแแแฎแแแแแแ 1623 แฌแแแก. Wilhelm Schickard, a German mathematician and clergyman, designed and built a mechanism which could add, subtract, multiply and divide. Schickard's machine was similar in operation to the slide rule but also incorporated a set of metal wheels that performed the arithmetical operations. Schickard called his device a "calculator-clock."