The famous Antikythera Mechanism, dateable to the first century B.C., demonstrates that intricate mechanical instruments were made in the Hellenistic period. While this instrument remained a unique survival, it was however possible to regard this type of artifact as highly unusual. More recently, a second Greek geared device has emerged. This instrument, known as the Byzantine Sundial Calendar, is of later date, from about 500 ad. It is very much simpler than the Antikythera Mechanism, but the existence of two instruments, using similar technology for comparable purposes, both in an astronomical context, encourages us to believe in a continuing tradition of making such devices in late antiquity. The author describes a “minimal” reconstruction of the Byzantine instrument, and shows that it must have been closely comparable to the arrangement of an instrument described in about 1000 ad by the polymath Al-Bīrūnī. This correspondence leads us on to suppose that the Hellenistic tradition of making geared instruments survived to be transferred to the world of Arabic learning. With the subsequent transfer of knowledge from Arabic culture to the Latin West, we have an unbroken chain of development from antiquity to modern technical achievements of the present day.