The documentary evidence comes from Ptolemy and Theon of Alexandria who explicitly says that Hipparchus wrote a work on chords in 12 books. However, Neugebauer points out that:
Ang dokumentasyon mula sa Ptolemy at Theon ng Alexandria na explicitly says na Hipparchus wrote isang trabaho sa Chords sa 12 mga libro. Gayunman, Neugebauer point out na: