The Z4 was arguably the world's first commercial digital computer. It was designed, and manufactured by early computer scientist Konrad Zuse's company Zuse Apparatebau, for an order placed by Henschel & Son, in 1942; though only partially assembled in Berlin, then completed in Göttingen, and not delivered by the defeat of Nazi Germany, in 1945. The Z4 was Zuse's final target for the Z3 design. Like the earlier Z2, it comprised a combination of mechanical memory and electromechanical logic, so was not a true electronic computer. Construction The Z4 was very similar to the Z3 in its design but was significantly enhanced in a number of respects. The memory consisted of 32-bit rather than 22-bit floating point words. The Program Construction Unit (Planfertigungsteil) punched the program tapes, making programming and correcting programs for the machine much easier by the use of symbolic operations and memory cells. Numbers were entered and output as decimal floating-point even though the internal working was in binary. The machine had a large repertoire of instructions including square root, MAX, MIN and sine. Conditional tests included tests for infinity. When delivered to ETH Zurich in 1950 the machine had a conditional branch facility added and could print on a Mercedes typewriter. There were two program tapes where the second could be used to hold a subroutine. (Originally six were planned.) In 1944, Zuse was working on the Z4 with around two dozen people, including Wilfried de Beauclair. Some engineers who worked at the telecommunications facility of the OKW also worked for Zuse as a secondary occupation. Also in 1944 Zuse transformed his company to the Zuse KG (Kommanditgesellschaft, i.e. a limited partnership) and planned to manufacture 300 computers. This way he could also request additional staff and scientists as a contractor in the Emergency Fighter Program. Zuse's company also cooperated with Alwin Walther's Institute for Applied Mathematics at the Technical University of Darmstadt. To prevent it from falling into the hands of the Soviets, the Z4 was evacuated from Berlin in February 1945 and transported to Göttingen. The Z4 was completed in Göttingen in a facility of the Aerodynamische Versuchsanstalt (AVA, Aerodynamic Research Institute), which was headed by Albert Betz. But when it was presented to scientists of the AVA the roar of the approaching front could already be heard, so the computer was transported with a truck of the Wehrmacht to Hinterstein in Bad Hindelang