The extension of 2D interactive graphics systems for geometric constructing in secondary schools through tools for interactive calculations on geometric configurations provides, from a didactic point of view, an opportunity for reflection and analysis. In this article the qualities will be presented which an interactive tool for calculating in planimetry could and should possess. With reference to examples the functioning of a prototype calculation module (calculation module of Cabri‐géomètre) will be described. A first evaluation will be made of the didactic potentialities involved and finally special and general problems of the use of such tools will be discussed.