Ptolemy was a mathematician, geographer, historian and astrologer who lived in Alexandria, Egypt during the latter part of the first century and early part of the second century AD. He was a Greek-Roman citizen and author who was associated with the great Alexandria Library. For our purposes, we are most interested in the Canon of Kings used by ancient astronomers to mark dates and times for astronomical obsevations and events like eclipses. His preservation of this list became one of the most important contributions to the study of ancient chronology.
The starting point of Ptolemy's Nabonassar era on Thoth 1 of the year 747 BC (February 26) is established by 19 lunar eclipses Therefore, we can locate any year of any of these kings as reckoned by the Egyptian calendar year, and we can compute that date in our own BC dating system.