From the establishment of Jesuit missions in the Argentine province of Chaco in the 18th century to nowadays the systems of measurement and counting of the Mocovi (who live on the territory of the Argentine Republic) have been influenced by the West. Ruptures and continuities in the interaction between two conceptions of measurement and quantification are the object of the present work which is based on a 1999 field study carried out in the communities of the colony Juan Larrea and Cacic Catan in the south-western Chaco region. It appears that the western way of quantifying the world prevails among the Mocovi and that this prevalence also enables to have this group under control.