The present manuscript preserves a copy of Aḥmad ibn Qāsim al-Šhāfi‘ī al-Ġhazzī's Kitāb Šarḥ Nuzha fī ‘Ilm al-Ḥisāb (The book of the explanation of the excursion in the science of calculus), a work that exemplifies the lively interest in the mathematical sciences that persisted in the Islamic world well after the end of the "classical" period that saw the flowering of Arabic sciences. Kitāb Šarḥ Nuzha fī ‘Ilm al-Ḥisāb is technically a supercommentary. Al-Ġhazzī ’s work is an explanation of Nuzhat al-Nuẓẓār fī ‘ilm al-Ġubār (The excursion of the observer in the science of numerals), which in turn was an abridgment by Aḥmad ibn Muḥammad al-Farāḍī ibn Al-Hā'im (around 1356-1412) of his own mathematical treatise entitled Muršida al-Ṭālib ilā Asnā al-Maṭālib (A student guide to the summit of learning). The original work, the abridgement, and the commentary all have an explicit didactic aim. The discussion of numerals and the treatment of the four arithmetical operations are presented in an incremental and extremely clear way. In the present manuscript, rubricated headings and passages underlined in red ink help the reader to identify the sections of the treatise and to distinguish between the original treatise by Ibn al-Hā'im and al-Ġhazzī's work. The latter is characterized by a large number of practical examples, with mathematical operations explained both in the text and displayed in tables.