With support in the works of Duval (2004) regarding the operation of conversion between semiotic registries, the studies of numerical “transcodification” are analyzed. It is stated that in the studies on the understanding process of the decimal system of numeration by children, it is convenient to relate the activity of conversion between the verbal and Hindu-Arabic registers to the operating activity of children, when they try to respond to the logical demands presented to them by the understanding of the syntax implied in the decimal system of numeration, as a form of revealing the mechanisms that govern the constructions built by the children in this field.