Greece, Ancient Greek Technology

Portable ringed sundial. The portable clock of Parmenion . Photo : Augusta Stylianou Artist

Three articulated rings are hung at an upright position with its external ring with an east-west orientation.
The central ring comprises of two semicircles (bearing 2 pairs of engravings of 7 grooves defining the months for 4 different geographical latitudes-towns). The inner ring bears a hole on its periphery, while around it there are engravings dividing it into 12 equal parts which define the 12 hours.
During the clock operation the semicircle with the data of the are is turned by 90╬Ž and the inner ring is put on the current month; thus a bright spot indicates the hour on the opposite side.
The clock can also be used at midday of the equinoxes in order to find the latitude of a place, the azimuth and the star height. (Fractions of the instrument were found in the Philippes' Octagon)