This chapter delves into the geometric mechanics underlying oblique axonometric projections. It focuses on the projection and restitution of coordinate systems, starting from an oblique projection of the standard triplet (O, x, y, z) onto a picture plane. Through analytical constructions and homological relationships, the chapter illustrates how to determine obliquity, evaluate projections of geometric elements, and calculate distortions. Emphasis is placed on the role of geometric reasoning in defining projection parameters and on how variations in angles and positions affect the resulting image. The chapter lays the groundwork for consistent and reproducible drawing practices in oblique axonometry.