It is hypothesized that contacts between the ancient Indian scholarly tradition and Hellenistic Greece via the Indo-Greek Kingdom after the Indian campaign of Alexander the Great, specifically regarding the work of Hipparchus (2nd-century BCE), explain some similarities between "Surya Siddhanta" and Greek astronomy in the Hellenistic period. For example, "Surya Siddhanta" provides table of sines function which parallel the Hipparchian table of chords, though the Indian calculations are more accurate and detailed. According to Alan Cromer, the knowledge exchange with the Greeks may have occurred by about 100 BCE. According to Alan Cromer, the Greek influence probably arrived in India by about 100 BCE. The Indians adopted the Hipparchus system, according to Cromer, and it remained that simpler system rather than those made by Ptolemy in the 2nd century.