The oldest known printed book on geometry in Dutch: 'Die waerachtige const der geometrien' (1513) In 1513 an anonymous work was issued from the press of Thomas van der Noot in Brussels, entitled Die waerachtige const der geometrien (The true art of geometry). So far as known this is the first book in Dutch on geometry to appear in print. It is a practical treatise in the tradition of the Roman agrimensores, and intended for surveyors and gangers. On account of Van der Noot's practice to print books translated by himself in Dutch, we can take for granted that he was also the compiler of Die waerachtige const. From a close examination of the text appears that his main source was book VI, De elementis geometriae, of Gregor Reisch's Margarita philosophica. Probably he used also Johann Widmann's Behende und hubsche Rechnung auff alien kauffmanschaft, besides other sources. A second edition of Die waerachtige const appeared in Antwerp by Jan Roelants in 1547.