Painting of the Italian mathematician Fra Luca Pacioli (1447-1517), demonstrating a theorem of Euclid to a young man at a table filled with geometrical tools, compass, slate, chalk and a dodecahedron model. Suspended above the slate is a glass rhombicubeoctahedron half-filled with water. As well as his published work written on geometry, arithmetic, and mathematical proportions, he was celebrated for his developments in accountancy, particularly his double-entry book-keeping system, becoming known as the father of accountancy. In 1496, Luca Pacioli was appointed by Ludovico Sforza as Milan's first chair of mathematics. At the Castello Sforza he met and befriended Leonardo da Vinci who was the artist to the court. Pacioli gave him mathematics lessons and, in return, Leonardo drew the illustrations (such as an icosahedron) for Pacioli's work, De Divine Proportione.