In 1714, the Italian violinist and composer Giuseppe Tartini discovered that when playing double stops on his violin, a third tone ("terzo suono") is produced. Tartini's investigations highlight the significance of this acoustic phenomenon in music theory and harmony, instrumental practice, and particularly for intonation. The "terzo suono" has intrigued musicians and musicologists for 300 years. With the development of theories, the terminology has also evolved: today, it is mostly referred to as combination tones. Angela Lohri demonstrates in her study how Tartini's "terzo suono" can be understood in light of both historical and contemporary research. The analysis of primary sources from Tartini to the mid-19th century provides the necessary foundation for further inquiries. Aspects related to the development of formulas and systematics are also addressed.