The teaching of harmonic foundations in music is a common learning objective in many education systems. However, music theory is often considered as a non-interactive subject matter that requires huge efforts to understand. With this work, we contribute a novel tangible device, called ScaleDial, that makes use of the relations between geometry and music theory to provide interactive, graspable and playful learning experiences. Therefore, we introduce an innovative tangible cylinder and demonstrate how harmonic relationships can be explored through a physical set of digital manipulatives, that can be arranged and stacked on top of an interactive chromatic circle. Based on the tangible interaction and further rich visual and auditory output capabilities, ScaleDial enables a better understanding of scales, pitch constellations, triads, as well as intervals. Further, we describe the technical realization of our advanced prototype and show how we fabricate the magnetic, capacitive and mechanical sensing.