La. Stat. tit. 13 § 583
The divisions provided in R.S. 13:582 shall be designated alphabetically as division "A," division "B," division "C," etc., and the presiding judges thereof shall be determined on July 31, 1946, in accordance with the following rules. The judge senior in point of continuous service shall preside over division "A," and the other judges of the district shall preside over the other designated divisions according to their respective periods of continuous service. In the event two or more judges in a district shall have served continuously the same length of time, the judge senior in age shall preside over the division first in alphabetical order of the divisions in question. Any additional divisions created after July 31, 1946, shall be given alphabetical designation in the order of their creation. The successor to any judge in a district shall preside over the same division as his predecessor.
La. R.S. § 13:583