What do you think was the greatest scientific advance of the hellenistic period? why?

The greatest scientific advancement of the Hellenistic period is the discovery of geometry. This is a discovery that had not only helped in astronomical calculations, but also helped in creating architecture. Geometry is still an important subject for us and so it is considered one of the most important discoveries during the Hellenistic period.  Astronomy is a subject that is highly dependent on geometry still today. Hellenistic period or civilization is considered one of the greatest civilizations that contributed hugely towards education.