In this article we attempt to demonstrate the relevance of certain theoretical concepts developed in mathematical didactique to the study of the process of teaching the skills for reading technical drawings for building construction. In particular, the concept of a fundamental situation makes it possible to pose the problem of the meaning of specific items of knowledge. The nature and degree of control required by the reading situation affect the meaning which the reader assigns to the graphics. We analyse the effectiveness of the reader and the quality of his controls with reference to invariants under orthogonal projection, a geometric notion which provides a theory of the relationship between objects in space and the viewer’s perception of them. The constitution of meaning of the graphics for the reader thus depends on the reading situations which be encounters, and on the controls which they necessitate. From a theoretical and methodological point of view, this engages us in two directions of analysis: analysis of working situations and analysis of training situations. In an interaction with these analyses, we have constructed a training process undertaking a rationalization of views of geometric order and reconstituting certain conditions of the workers’situations. The didactical analysis of reading situations for this process uses the concepts of didactical variable, informational jump and epistomological obstacle. In closing, we pose the problem of the conditions of viability of such a process as it encounters the current tendencies of training.