1 Chronicles 27:2
Over the first course for the first month was Jashobeam the son of Zabdiel: and in his course were twenty and four thousand. Over the first course for the first month was Jashobeam the son of Zabdiel: and in his course were twenty and four thousand.
The list in 1 Chronicles 27:1-15 sets out twelve monthly courses that made up the standing regular army, and the first month's course under Jashobeam the son of Zabdiel numbered twenty-four thousand men. The division into twelve monthly courses shows the year to consist of twelve months. Counted together those twelve courses give a year of three hundred sixty days, reckoned as twelve months of thirty days each.
The regular army enrolled in these courses explains the difference between the totals in 1 Chronicles 21 and 2 Samuel 24, since the census in Samuel left out the regular army that the census in Chronicles included. At the same time those figures may contain a copyist's transcription error.