This article examines three so far unknown lemmatic commentaries on computus and on astrolabe topics, which are to be found in MS Stuttgart, Württembergische Landesbibliothek, Cod. math. 4 degrees 33 (second half of the twelfth-century). The commentaries are on the 'Compotus' by Gerlandus, on the 'De mensura astrolabii' by Hermann of Reichenau, and on the 'De utilitatibus astrolabii', which is sometimes attributed to Gerbert of Aurillac. No commentaries on the respective treatises have previously been identified as such. The commentaries of the Stuttgart manuscript are of special interest in that they allow us to understand how a twelfth-century scholar read works on computus and the astrolabe, namely works that date back to the eleventh century. Their author remains anonymous, but in all probability he wrote his commentary on the 'Compotus' by Gerlandus either in 1143 or in 1150. An appendix to the article includes transcriptions of the introductory texts on the computus and on the astrolabe as well as the beginnings of the commentaries.