This manuscript of Ma’aseh ḥoshev (The art of calculation), one of the most valuable Hebrew codices in the Bavarian State Library, is arranged in 24 separate works or grouped fragments of texts on mathematics, geometry and astronomy, together with a great number of explanatory notes, glosses, and additions. It is hard to do justice in a few words to the very broad range of matters discussed, which, in the disciplines covered, reflect the state of scientific knowledge in the Middle Ages. The work was compiled and mostly written by Levi ben Gershom, also known as Gersonides and by the acronym Ralbag (1288‒1344), in 1321. The largest part of the 265 paper leaves is taken up by the works of Euclid, including fragments of his treatises on optics and catoptrics, and especially the Elements, with commentaries by al-Farabi and Ibn al-Haitam translated by Mosheh Ibn Tibon. One of the most important texts is the Mishnat ha-Middot (Theory of measures), held to be the oldest Hebrew work on geometry, which dates from about 150. The manuscript also contains texts by other great Jewish scholars of the Middle Ages, such as Abraham bar Hiyya Savasorda (died circa 1136), Abraham ben Meïr Ibn Esra (1089‒1164), Simon Motot (15th century), and Mordecai ben Eliezer Comtino (1420‒circa 1487). The main part of the manuscript was transcribed in Constantinople in 1480 by a certain Moses ben David, who mentions his name on folios 100 verso and 173 verso. The manuscript came from the collection of Johann Albrecht Widmannstetter to the ducal court library in Munich, the present-day Bavarian State Library.