Using the information in Kings and Chronicles, Edwin Thiele calculated the dates of the reigns of the kings of Judah from the division of the kingdom, which he calculates to have been in 931–930 BCE. Thiele noticed that for the first seven kings of Israel (ignoring Zimri's seven-day reign), the synchronisms to Judean kings fell progressively behind by one year for each king. Thiele saw this as evidence that the northern kingdom was measuring the years by a non-accession system (first partial year of reign was counted as year one), whereas the southern kingdom was using the accession method (it was counted as year zero). He also concluded that the calendars for reckoning the years of kings in Judah and Israel were offset by six months, that of Judah starting in Tishri (in the fall) and that of Israel in Nisan (in the spring). This is the conclusion from cross-synchronizations between the two kingdoms which often allows the narrowing of the beginning and/or ending dates of a king within a six-month period, identifying the difference as due to the calendar starting date. Once these were understood, the various reign lengths and cross-synchronisms for these kings was determined, and the sum of reigns for both kingdoms produced 931/930 BCE for the division of the kingdom when working backwards from the Battle of Qarqar in 853 BC.