Mashallah's treatise on the astrolabe (p 10) is the first known of its kind. Later translated from Arabic into Latin ("De Astrolabii Compositione et Ultilitate"). The exact source of Geoffrey Chaucer's Treatise on the Astrolabe (1391) in Middle English is undetermined but most of his ‘conclusions’ go back, directly or indirectly, to a Latin translation of Mashallah's work, called "Compositio et Operatio Astrolabii". Chaucer's description of the instrument amplifies Mashallah’s, and his indebtedness was recognised by John Selden in 1613 and established by Walter William Skeat. While Mark Harvey Liddell held that Chaucer drew on "De Sphaera" of John de Sacrobosco for the substantial part of his astronomical definitions and descriptions, the non-correspondence suggests his probable source was another compilation. Skeat's "Treatise of the Astrolabe" includes a collotype MS facsimile of the Latin version of the second part of Mashallah’s work, which parallels Chaucer's. This is also found in R. T. Gunther's, "Chaucer and Messahala on Astrology".