The Stimmeinstellungszeichen, literally “voice disposition indicators,” are metal shapes about 10 cm in diameter. Polished brass wire is bent to form abstract curves and lines. The linguist Eduard Sievers invented them to support his system of sound analysis (Schallanalyse). From 1910, Sievers was a follower of Joseph Rutz’s theory: Rutz identified four different types of voices, which he connected to different states of activation of the trunk muscles and to the four traditional temperaments (sanguine, phlegmatic, choleric, and melancholic). Sievers modified this theory by adding more voice types and various subcategories. He believed that a particular muscular activation could be provoked by having the speaker focus on mathematical line constructions. According to Sievers, simply looking at these shapes evokes an idea of traction and pressure, to which the muscular system reacts. Sievers was inspired by the sideric pendulum, introduced to him by his student Rolf Blümel, who also made the first versions of the indicators. Presenting eleven of these metal shapes in his first study in 1914, by 1918 Sievers had expanded the repertoire to thirty-two.