1 Chronicles 27:6
This is that Benaiah, who was mighty among the thirty, and above the thirty: and in his course was Ammizabad his son. This is that Benaiah, who was mighty among the thirty, and above the thirty: and in his course was Ammizabad his son.
1 Chronicles 27:1-15 sets out David's regular army divisions arranged by monthly courses, and this verse belongs within that list. The list presents twelve divisions for twelve months, showing that the Bible recognizes twelve months in a year. Israel's months were regulated by the new moons rather than by fixed days of the week, and its annual feasts were therefore regulated in the same way.
The list of regular divisions describes a force that was somewhat smaller at that time. That regular force may account for the difference between the army totals in 1 Chronicles 21 and 2 Samuel 24. The reckoning in Chronicles may have included the regular army, while the reckoning in Samuel did not include it.