Contains the Greek text, with parallel French translation, of a manuscript detailing how to use an astrolabe. The Greek language manuscript is itself a translation of a Latin manuscript, which is a translation of an Arabic text attributed to Messahalla. The authors believe that the Greek manuscript was copied around 1309 in Byzantium (by an unknown person), at which time two completely new Greek chapters were added. The Greek manuscript is one of many manuscripts, which, compiled together, form the larger manuscript Oxoniensis Cromwellianus 12, housed at Oxford's Bodleian Library. The texts are accompanied by commentary.