Levi ben Gerson (1288-1344)wrote Book of Numbers in 1321 dealing with arithmetical operations, including extraction of roots. Also, in 1342, he wrote On Sines, Chords and Arcs which examined trigonometry, in particular proving the sine theorem for plane triangles and giving 5 figure sine tables.

One year later, at the request of the bishop of Meaux, he wrote The Harmony of Numbers which is a commentary on the first 5 books of Euclid.

He also invented Jacob's staff, an instrument to measure the angular distance between celestial objects. It is described as consisting

... of a staff of 4.5 feet (1.37 m) long and about one inch (2.54 cm) wide, with six or seven perforated tablets which could slide along the staff, each tablet being an integral fraction of the staff length to facilitate calculation, used to measure the distance between stars or planets, and the altitudes and diameters of the Sun, Moon and stars.

Levi observed a solar eclipse in 1337. After he had observed this event he proposed a new theory of the sun which he proceeded to test by further observations.

Another eclipse observed by Levi was the eclipse of the Moon on 3 October 1335. He described a geometrical model for the motion of the Moon and made other astronomical observations of the Moon, Sun and planets using a camera obscura.

Some of his beliefs were well wide of the truth such as his belief that the Milky Way was on the sphere of the fixed stars and shines by the reflected light of the Sun.

His other work was philosophical and he wrote complex Biblical commentaries.

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