the earliest Babylonian astronomer known by name, who devised the so-called System A, a group of ephemerides, or tables, giving the positions of the Moon, Sun, and planets at any given moment. Based on centuries of observation, these tables were nonetheless somewhat crude and were superseded about a century later by Kidinnu's (Kidinnu) System B, a refined mathematical method for finding celestial positions more accurately. Both systems were in use simultaneously between 250 and 50 BC. Nabu-rimanni also calculated the length of the synodic month (from New Moon to New Moon) to be 29.530614 days, as compared with the modern value of 29.530596 days.