We are using a duo of artefacts, constituted by a mechanical arithmetic machine and its digital counterpart, to enable six-year old French students to learn about numbers. The experiment shows the separate conceptualisation processes involving numbers as sign of a quantity and number sequences on one side and recursive addition, computation and its effect on the decimal code for numbers on the other side. The duo of artefacts enabled the design of situations that required these processes to be connected. We observed how students and teachers used the duo and discuss the results concerning the conceptualisation of number.