 "Kalkül" is the German term for a formal system—as in "Hilbert-Kalkül", the original name for the Hilbert-style deduction system—so "Plankalkül" refers to a formal system for planning.In the domain of creating computing machines, Zuse was self-taught, and developed them without knowledge about another mechanical computing machines that existed already.To describe logical circuits, Zuse invented his own diagram and notation system, which he called "combinatorics of conditionals" ().