What is the contribution of Georg Von Purbach in trigonometry?

Answer 1

In Epytoma…in Almagestum Ptolomei, the abridgment of Ptolemy's Almagest which was completed by his student, Regiomontanus, he replaced chords by sines, and calculated tables of sines for every minute of arc for a radius of 600,000 units. He made his observations with very simple instruments, using an ordinary plumb-line to measure the angles of elevation of the stars. He also introduced a mathematical innovation by using Hindu-Arabic numerals in his sine tables, the first transition from the duodecimal to the decimal system. Peuerbach noted several errors in Ptolemy's calculations, but remained a devotee of the ancient Greek mathematician.