The calculator offered here is from 1973 and bought directly from Hewlett Packard in California. It is in very good condition. Al calculation functions work. The battery pack has been exchanged by a new item in 2011. The instructions on the back side are in German language. The HP-35 electronic pocket calculator was produced by the American company Hewlett-Packard between 1972 and 1975 as the world's first scientific calculator with trigonometric, logarithmic, and exponential functions. It received its short name "HP-35" from company head Bill Hewlett (1913-2001) because of its 35 keys. In 1972, the calculator cost around 2,000 Deutsche Marks in Germany (approximately €3,400 today). With dimensions of approximately 15 x 8 centimeters, the calculator fits comfortably in any jacket pocket, hence the name "pocket calculator." The calculator use a conventional floating-point display to show numbers, which automatically switched to scientific exponential notation for larger values. Internal calculations used a 14-digit binary code (BCD numbers). Reverse Polish Notation (RPN) was chosen for faster input, minimizing keystrokes by eliminating parentheses.