This paper focuses on drawings in Zarlino's theoretical writings which combine iconic with diagrammatic elements to convey musical concepts and theories. Several drawings of monochords and lutes deal with equal temperament and incommensurability. Two pictures from the Sopplimenti musicali (1589), have received little attention to date. They are related to musical experimental devices, called heliconae, which are discussed in detail in Ptolemy's Harmonics. Knowledge of geometric similarity theory is necessary to understand these devices. Zarlino's drawings feature the cube, a Pythagorean triangles and a circular diagram to prove the universality of his “senario”, the extension of the Pythagorean tetraktys from four to six mutually related entities. In doing so, he argues from a continuous perspective, similar to Johannes Kepler later, who tries to “prove” the same set of consonances, i.e., a special algebraic constellation with a compass and ruler argument.
In the presentation of this paper, Ptolemy's and Zarlino's heliconae were also be demonstrated as virtual instruments.