As is often the case, understanding comes with an understanding of the culture. Here, the regnal numbers of the Kings becomes apparent, Thiele tells us, by taking into account these basic considerations:

• Accession-year dating. Certain ANE cultures, when a king began his reign in the middle of a calendar year, did not consider this to be the monarch's first year, but rather called this an accession year, and began the first year of the reign from the first of the next calendar year. (This would be equivalent to a President’s first year being counted from the January following his appointment, even though he assumed office in the previous June.)
• Co-reigns. As today, a king may appoint his son as co-regent while still alive.
• Different starts of regnal years. Problematically, Israel and Judah started their regnal years in different months for most of their history - although Judah switched methods for part of their history, which has contributed greatly to the confusion!

Thiele takes these and other considerations into account, and the result is stupendous. Not only does he achieve a chronology for the Hebrew kings that accords with the Bible; he also makes a perfect fit with records of other cultures. This truly amazing project is one of a kind, and is well worth being acquired - even if you have no particular need for the material.