In the absence of the Arabic text of al-Khw's Arithmetic, which has not yet been found, the oldest Latin adaptations from the twelfth century are the only evidence documenting the genesis and the first spreading of a decimal arithmetic that uses nine figures and zero, i.e. the Indian reckoning known in the Middle Ages as algorismus. This paper studies these texts, their content, their sources, and identifies their authors and the milieus in which they were written.