Qūshjī presented al-Risāla al‐Muḥammadiyya fī al‐ḥisāb (The Muḥammadiyya Treatise on Arithmetic) to the Ottoman Sultan Mehmet II upon his arrival in Istanbul in 877/1473. The treatise, named in the Sultan’s honor and dedicated to him, is an expanded revision in Arabic of Qūshjī’s Persian Risāla dar ʿilm-i ḥisāb, which he wrote in Samarqand. Both works were studied in Ottoman madrasas. And Kātib Çelebī (d. 1067/1657) wrote a commentary on the introduction of the Muḥammadiyya entitled Aḥsan al-hadiyya, which he taught. al-Risāla al‐Muḥammadiyya is composed of two parts: part one (an introduction and 5 chs.) deals with arithmetic/calculation (ḥisāb); part two (an introduction and 3 chs.) deals with measurement (misāḥa). In Part One, Qūshjī provides detailed definitions and analyses of concepts and terms (such as arithmetic, number, unit) as well as explanations of mathematical methods/operations (for example, the “rule of double false position” [al-ḥisāb al-khaṭaʾayn], used to find solutions to a linear equations). An important feature of the work is Qūshjī’s introduction into Islamic mathematics (perhaps borrowed from Chinese mathematics) of the added use of the terms “positive/muthbat” and “negative/manfī” for the two terms addition (“plus/zāʾid”) and subtraction (“minus/nāqis”); the terms were transmitted by Byzantine mathematicians to Europe and translated into Latin as positivus and negativus. With his emphasis on calculation and mathematical exactitude, Qūshjī functional approach to mathematics contributed to the elimination of Hermetic–Pythagorean numerical mysticism from Ottoman mathematics.