15th- and 16th-century mensural notation raises many debates and questions among musicologists and modern performers. The contradictory teachings found in the vast body of theory from the Renaissance can be addressed through a better understanding of the treaties' roles as well as the highlighting of the mechanisms that turn a descriptive system in a set of prescriptive and self-referential rules disconnected from musical practice: the cult of authority, a wish for symmetry and a taste for completeness. Meanwhile, the exploration of the links between tactus and counterpoint makes it possible to define the active time window in which the management of dissonances becomes a dynamic process. The sliding cursor where the Notenbild is scrolled allows for an internal examination of the music that clarifies most of the ambiguities regarding choice of tempo while avoiding the pitfalls of theoretical contradictions.