It depicts the Franciscan friar Luca Pacioli, mathematician and student of proportions, while he carries out one of the problems of geometry reported in Euclid's Elements. Next to him an elegant young man who could be identified with Guidobaldo da Montefeltro. On the green table are arranged the tools of the trade, the compass, the protractor, the chalk, the sponge, the open book of Euclid and a closed one on which the letters LI.R.LUC.B stand out, to be dissolved with this inscription: Liber reverend Lucae Burgenis, which would refer to the Summa de Arithmetica, Geometria, Proportione, mathematical treatise by Luca Pacioli, published in Venice in 1494 and dedicated to Guidobaldo. Suspended from a thread hangs a transparent polyhedron which reflects a building very similar to the Ducal Palace in Urbino.