The outer portion of the front of the astrolabe labeled with Roman numerals. The Roman numerals represent the twenty-four hours of the day. In Medieval times, the mater acted as a "holder" for the latitude plates, which could be removed and replaced.
A thick, round plate on an astrolabe with a shaped projection to take the suspension ring and which houses discs of brass engraved with scales.
part of an astrolabe, see article on the astrolabe.