The system works like this. You get credit for the overtime you work. The people with the least amount of worked overtime are at the top of the list, and the most are at the bottom.

When opportunities for overtime are offered, we work down the list starting with the people who have worked the least overtime.

If we go though the list twice, and the number of people requested to work isn't fulfilled, whoever is at the top is then forced to work the overtime. And we do that until we have the people.